Modding Tutorials

Tutorials on how to mod NSMB DS

Mario vs Luigi
Modding 101 - Creating a Bare-Bones Level

Mario vs Luigi

This page documents how to play MvsL hacks and objects that work in MvsL.

Modding MvsL is significantly more difficult than modding Singleplayer levels. If you're just getting started with modding the game, you might want to start here

FaQ

How do I play Mario vs Luigi hacks?

The easiest way to play an MvsL hack on real hardware is by using “Multi-cart”
- This requires that you own two flashcards (such as an R4 Card).
- To set this method up, simply put the same ROM on both flashcards. Then, in the game, choose the option to “Compete with another New Super Mario Bros. Owner” and play MvsL as you normally would.

If you do not have access to two flashcards, then you have two, more difficult, options remaining
- Your first option is to try and use a hacked NDS firmware that bypasses Download Play's signature check
  1. Download firmware.nds and put it on your flashcard.
  2. Open this ROM on the DS you will launch Download Play from.
  3. Now, eject the flashcard from the DS you just ran the ROM on. (This will not cause your DS to freeze)
  4. Finally, put the flashcard back in the other DS.
  5. Once you have done this, you can run the ROM of the MvsL hack and select “Play with someone who doesn't own New Super Mario Bros”
    - If the firmware ROM does not work on your flashcard, try this one instead.
- Your final option is to use normal DS Download Play with “DLP Mode” in NSMBe 5
  1. Open a clean (unedited) ROM
  2. Open it in NSMBe
  3. After you open the ROM, go to Tools and check “Enable DLP-friendly mode”
  4. Now, you can make whatever changes you want to the ROM
  5. When you're done, you can play with another DS through DS Download Play like you normally would using the “Play with someone who doesn't own New Super Mario Bros” option
If the game hangs at the Nintendo logo, you might have missed a step. Double check you did everything and try again with another clean ROM
If the DS freezes with a black screen after you select a level it can mean one of two things:
- Your flashcard is not compatible with this method.
  - Some flashcards don't like firmware.nds. Try using firmwarefix.nds instead.
- There's something wrong with the level that is making the game freeze

My level crashes, what do I do now?

If you are not using any Code Hacks, then here are some things to consider
1. Have you changed any object banks? This causes MvsL to crash so you need to change the object banks back to whatever the level had originally.
2. Double-check that you are not using an object that has been confirmed to crash MvsL. There is a table later on this page that shows what objects are compatible with MvsL.
3. Have you changed the number of Battle Stars that are in the level? Changing the number of Battle Stars in a level can cause MvsL to crash, and you will need to restore the original amount of Battle Stars the level had.

My level crashes, but I'm using Code Hacks!

Even with Code Hacks, not all objects work in MvsL. Take a look at the table at the end of the page to see if all of the objects you're using are compatible with MvsL.

My level makes us de-sync, what's going on?

Because of the nature of how multiplayer works in this game, the Random Number Generator seed is only synchronized once when the connection is established. Only inputs are sent from one console to another, so the code must account for both player actors. If code does not account for each player, the games will become de-synced. For example, if an enemy was coded to imply get the values of a player on the local console, it will read different data on each console. This causes the enemy to act differently on each DS, thus causing a de-sync.

Implementation example:
```
// Enemy reads only the position of its own console player
playerPositionX = Game::getPlayer(Game::localPlayerID)->position.x;
// Now the position that was read is different between both consoles
// for this enemy and he will behave differently for each console!
// This is very bad!

// A solution would be to get the position of the closest player
playerPositionX = enemy->getClosestPlayer(nullptr, nullptr)->position.x;
// This way, it gets the closest player instead of its console player
```

Object Compatibility (Vanilla)

These objects will work in MvsL regardless of if you are using code hacks
Most of the objects in this list are objects that are already used in MvsL

Object ID	Actor Name
23	Pipe Piranha Plant (Facing up)
24	Pipe Piranha Plant (Facing down)
25	Pipe Piranha Plant (Facing right)
26	Pipe Piranha Plant (Facing left)
27	Bill Blaster (Bullet Bill launcher)
28	Bob-omb
71	Stonewall moving up & down
72	Stonewall moving left & right
95	Spin Block
148	Goomba
149	Koopa Troopa
210	MvsL Big Star

Object Compatibility with Code Hacks

This spreadsheet is based on the nospritesetlimitation.s code patch
- To fix liquids in MvsL, use mvslLiquidFix.cpp
There are 4 kinds of compatibility
- Works: This object completely works in MvsL
- Partial: Some parts of this object do not work in MvsL. The notes column will mention what doesn't work
- N/A: The object does not load but it also does not crash the game
- Crash: The object crashes the game when loaded. See the notes for possible workarounds.

Object ID	Object Name	Compatibility	Notes
0	Crash Object (Player Actor)	Crash	Needs the clone code hack
1	Crash Object (Player Actor)	Crash	Needs the clone code hack
2	Crash Object (Player Actor)	Crash	Needs the clone code hack
3	Crash Object (Player Actor)	Crash	Needs the clone code hack
4	Crash Object (Player Actor)	Crash	Needs the clone code hack
5	Crash Object (Player Actor)	Crash	Needs the clone code hack
6	Crash Object (Player Actor)	Crash	Needs the clone code hack
7	Crash Object (Player Actor)	Crash	Needs the clone code hack
8	Crash Object (Player Actor)	Crash	Needs the clone code hack
9	Crash Object (Player Actor)	Crash	Needs the clone code hack
10	Nothing	N/A	Technically works due to it being nothing
11	Nothing	N/A	Technically works due to it being nothing
12	Nothing	N/A	Technically works due to it being nothing
13	Nothing	N/A	Technically works due to it being nothing
14	Nothing	N/A	Technically works due to it being nothing
15	Nothing	N/A	Technically works due to it being nothing
16	Nothing	N/A	Technically works due to it being nothing
17	Nothing	N/A	Technically works due to it being nothing
18	Nothing	N/A	Technically works due to it being nothing
19	Nothing	N/A	Technically works due to it being nothing
20	Defunct Actor 22	N/A	If using the Actor Spawner code hack it works
21	Mega Goomba	Works	If using Boss Particle code hack
22	Hammer Brother from map	N/A	MvsL is missing a world map so...
23	Pipe Piranha Plant (facing up)	Works
24	Pipe Piranha Plant (facing down)	Works
25	Pipe Piranha Plant (facing right)	Works
26	Pipe Piranha Plant (facing left)	Works
27	Bill Blaster (Bullet Bill launcher)	Works
28	Bob-omb	Works
29	Princess Peach	Works
30	Monty Tank	Works	If using Boss Particle code hack
31	Cheep Cheep	Works
32	Goal Pole's Flag	Works
33	Trampoline (portable springboard)	Crash
34	Red Ring	Crash
35	Final Bowser Controller	Crash
36	Thwomp	Works
37	Spiny	Works
38	Boo	Works
39	Castle boss controller	Partial	Some of the options crash the game, you can use a switch instead.
40	Lakitu (unused object)	Works
41	Bowser bridge switch	Works	Loads, but graphics are not loaded correctly
42	Chain Chomp/Log	Works
43	Chain Chomp (unused object)	Works
44	Fire Snake (unused Actor 46)	Works
45	Respawnable Hidden Block	Works
46	Event controller - activates Spiked Ball when touched by Snake Block	Works
47	Lakithunder	Works
48	Aquatic bubble current (up)	Works
49	Aquatic bubble current (down)	Works
50	Aquatic bubble current (right)	Works
51	Aquatic bubble current (left)	Works
52	Buzzy Beetle	Works
53	Dry Bones	Works
54	Lava Bubble (Podoboo)	Works
55	Bullet Bill Spawner	Works
56	Fire Bar	Works
57	Coin	Works
58	Bowser	Works
59	Hammer Brother	Works
60	Nothing	N/A	Technically works due to it being nothing
61	Nothing	N/A	Technically works due to it being nothing
62	Big Bowser (unused object)	Works
63	Dry Bowser	Works
64	Whomp	Works
65	Cheepskipper	Works
66	P Switch	Works	Graphics are not loaded correctly
67	Sushi (shark)	Works
68	Lift moving up and down	Works
69	Lift moving left and right	Works
70	Rotating log lift (unused actor)	Works
71	Stonewall moving up and down	Works
72	Stonewall moving left and right	Works
73	Wobbly metal lift	Works
74	Wobble Rock	Works
75	Seesaw lift	Works
76	Scale lift	Works
77	Flimsy Lift (falls once touched)	Works
78	Lift moving one way once stood on	Works
79	Three-platform rickshaw lift (rotates in place by self)	Works
80	Lift spawner	Works
81	Nothing	N/A	Technically works due to it being nothing
82	Rotating rectangle lift	Works
83	Self-activating block	Works
84	Zoom	Works
85	Flip fence (duplicate object)	Works
86	Rotating triangle lift	Works
87	Nothing	N/A	Technically works due to it being nothing
88	Brick Block containing P Switch	Works	P-Switch graphics are not loaded correctly
89	Snailicorn	Works
90	Wiggler	Works
91	Track-controlled lift	Works
92	Unagi (eel)	Works
93	Arrow signboard	Works
94	Swooper	Works
95	Spin Block	Works
96	Seaweed	Works
97	Nothing	N/A	Technically works due to it being nothing
98	Camera vertical scrolling	N/A
99	Four-platform rickshaw lift	Works
100	Vertical camera offset (unused actor)	N/A
101	Event controller - view enter	Works
102	Spiked Ball	Works
103	Dorrie	Works
104	Tweester (Tornado)	Works
105	Whirlpool	Works
106	Red Coin	Crashes
107	? Switch	Works	Graphics are not loaded correctly
108	! Switch	Works	Graphics are not loaded correctly
109	Amp	Works
110	Brick Block containing !-Switch	Works	!-Switch graphics are not loaded correctly
111	Floating log	Works
112	Nothing	N/A	Technically works due to it being nothing
113	Cheep Chomp	Works
114	Burner (Small)	Works
115	Large Spiked Ball	Works
116	Skeeter (Water Bug)	Works	Causes a desync however
117	Map Flying ? Block	N/A
118	Burner	Works
119	Swinging lift (pendulum-like)	Works
120	Grounded Piranha Plant	Works
121	Nothing	N/A	Technically works due to it being nothing
122	Big Grounded Piranha Plant	Works
123	Grounded Fire Piranha Plant	Works
124	Large grounded Fire Piranha Plant	Works
125	Defunct Actor 229	N/A
126	Drawbridge lift	Works
127	Big four-platform rickshaw lift	Works
128	Warp Cannon	Works
129	Boss Key Location	Works
130	Jumping Cheep Cheep	Works
131	Checkpoint - vertical	Works	Does the animation but doesn't set anything
132	Checkpoint	Works	Does the animation but doesn't set anything
133	Nothing	N/A	Technically works due to it being nothing
134	Nothing	N/A	Technically works due to it being nothing
135	Nothing	N/A	Technically works due to it being nothing
136	Pokey	Works
137	Nothing	N/A	Technically works due to it being nothing
138	Nothing	N/A	Technically works due to it being nothing
139	Nothing	N/A	Technically works due to it being nothing
140	Boss Key	Works
141	Swelling ground	Works
142	Tightrope	Works
143	Spiked ? Block (unused actor 251)	Crashes
144	Spiked ? Block	Crashes
145	Spiked ? Block (unused actor 253)	Crashes
146	Ground-pound panel	Works
147	Bump from below platform	Works
148	Goomba	Works
149	Koopa Troopa	Works
150	Koopa Paratroopa	Works
151	Nothing	N/A	Technically works due to it being nothing
152	Event trigger block	Crash
153	Nothing	N/A	Technically works due to it being nothing
154	Nothing	N/A	Technically works due to it being nothing
155	Special exit controller (warp entrance)	Crash	Sometimes just corrupts graphics and does nothing
156	Nothing	N/A	Technically works due to it being nothing
157	Fire Brother	Partial	Causes a desync
158	Boomerang Brother	Partial	Causes a desync
159	Nothing	N/A	Technically works due to it being nothing
160	Nothing	N/A	Technically works due to it being nothing
161	Nothing	N/A	Technically works due to it being nothing
162	Mushroom Platform lift	Works
163	Nothing	N/A	Technically works due to it being nothing
164	Event controller - "AND"	Works
165	Event controller - "OR" (If X OR Y, do Z)	Works
166	Event controller - "RANDOM"	Works
167	Event controller - chainer (If X, do Y)	Works
168	Event controller - "IF" (uses zones)	Works
169	Spin Block (unused Actor 255)	N/A	Doesn't spawn
170	Nothing	N/A	Technically works due to it being nothing
171	Spin Block (unused Actor 256)	N/A	Doesn't Spawn
172	Nothing	N/A	Technically works due to it being nothing
173	Swinging/able rope	Works
174	Mushroom Platform lift	Works
175	Bouncy bricks (Unused)	Works
176	Nothing	N/A	Technically works due to it being nothing
177	Nothing	N/A	Technically works due to it being nothing
178	Nothing	N/A	Technically works due to it being nothing
179	Nothing	N/A	Technically works due to it being nothing
180	Climbing Koopa	Works
181	Nothing	N/A	Technically works due to it being nothing
182	Nothing	N/A	Technically works due to it being nothing
183	Lakitu spawner	Works
184	Nothing	N/A	Technically works due to it being nothing
185	Cheep Cheep random spawner	Works
186	Paragoomba	Works
187	Balance lift	Works
188	Nothing	N/A	Technically works due to it being nothing
189	Pipe Cannon	Works	Desynchronizes the game
190	Nothing	N/A	Technically works due to it being nothing
191	Hanging Bouncing ? Block	Works
192	Coin Spawner (unused actor)	Crash
193	Big Dry Bones	Works
194	Big Thwomp	Works
195	0 Stick to bottom length activator left	Works
196	0 Stick to bottom length activator right	Works
197	Tile Creator/Destroyer (Tile God)	Crash
198	In air vertical scroll stop left	N/A
199	In air vertical scroll stop right	N/A
200	Nothing	N/A	Technically works due to it being nothing
201	Nothing	N/A	Technically works due to it being nothing
202	Nothing	N/A	Technically works due to it being nothing
203	Unused Purple Mushroom Platform Lift	Works
204	Fire Snake	Works
205	Flame Chomp Spawner	Works
206	Ghost house goo	Works
207	Big Cheep Cheep	Works
208	Nothing	N/A	Technically works due to it being nothing
209	Sledge Brother	Works	Causes a desync however
210	MvsL Battle Star	Works	Who would've thought
211	Blooper	Works
212	Blooper Nanny (unused actor 144)	Works
213	Blooper Nanny that w/ Baby Bloopers	Works
214	Nothing	N/A	Technically works due to it being nothing
215	Nothing	N/A	Technically works due to it being nothing
216	Nothing	N/A	Technically works due to it being nothing
217	Nothing	N/A	Technically works due to it being nothing
218	Auto-scrolling controller	Works	If the players spawn in the same position after respawning it stops working
219	Spike Top	Works
220	Bowser Jr.	Works
221	Nothing	N/A	Technically works due to it being nothing
222	Mini Goomba	Works
223	Flip fence	Works
224	Big flip fence	Works
225	Nothing	N/A	Technically works due to it being nothing
226	Scuttlebug	N/A
227	Moneybag	Works
228	Roulette Block	Crash
229	Petey Piranha	Works
230	Nothing	N/A	Technically works due to it being nothing
231	Water	Works
232	Hanging ? Block	Works
233	Swinging/able pole	Works
234	Lava	Partial	Causes a desync is not using mvslLiquidFix.cpp
235	Star Coin	Crash
236	Rotating square lift	Works
237	Broozer	Works
238	Purple Mushroom Platform lift	Works
239	Yellow/Orange Mushroom Platform	Works
240	Nothing	N/A	Technically works due to it being nothing
241	Bill Blaster Turret	Works
242	Blue Mushroom Platform	Works
243	Roof Spiny	Works
244	Bouncy Mushroom Platform	Works
245	Corked Pipe + foot pump	Crashes
246	Floating barrel	Works
247	Sushi spawner (shark spawner)	Works
248	Balloon Boo	Works
249	Track-controlled wall-jump lift	Works
250	Crowber	Works
251	Big Unagi	Crash
252	Banzai Bill Blaster	Works
253	Nothing	N/A	Technically works due to it being nothing
254	Kab-omb	Works
255	Jungle FG Effect (Unused Actor)	Works
256	Rotating carry-through-wall turntable-like lift	Works
257	Coin trail Cheep Cheep	Works
258	Spike Bass (unused object)	Works
259	Poisoned Water	Partial	Causes desync if not using mvslLiquidFix.cpp
260	Fast Spike Pillar - Down	Works
261	Fast Spike Pillar - Up	Works
262	Fast Spike Pillar - Left	Works
263	Fast Spike Pillar - Right	Works
264	Mega Ground Pound's sky drops +	Crash
265	Phantom Hand (Pointing hand)	Works
266	Invisible Lava Bubble (unused actor)	Works
267	Nothing	N/A	Technically works due to it being nothing
268	Underwater bounce bubble	Works
269	Giant Wiggler	Works
270	Smashed pipe object	Works
271	Crowber spawner	Works
272	Snowy branch	Works
273	Snow Spike	Works
274	Sinking-snow pile	Works
275	Blockhopper	Partial	Desyncs
276	Scroll and Mario stop sideways	Works
277	Arrow sign	Works
278	Groundpound-able ghost house goo	Works
279	Flipper (one-way gate)	Works
280	Horizontal camera offset	N/A	Not sure how this object works
281	Squiggler	Works
282	Swinging/able vine	Works
283	Spike Bass spawner	Works
284	Splunkin (pumpkin)	Works
285	Scuttlebug spawner	N/A
286	Event controller - multi-chainer	Works
287	Enemy-in-Pipe Generator	Works
288	Nothing	N/A	Technically works due to it being nothing
289	Platform Block (expandable block)	Works	Doesn't respawn if it turns into bricks and you collect a battle star.
290	Flying ? Block	Crash	Black screen
291	Brick Block containing ? Switch	Works	? Switch graphics are not loaded correctly
292	Event Activated Door	Works
293	Touching ground vertical scroll stop left	Works
294	Touching ground vertical scroll stop right	Works
295	Mummipokey	Works	Use a P-Switch
296	Lift moving left and right	Works
297	Stonewall moving left and right	Works
298	Stonewall moving u, d, l, r	Works
299	Snake Block	Works
300	Haunted lift	Works
301	Toadsworth	Works	Only freezes Mario for a few seconds, and Luigi can roam freely. Background chooser will break because of BMG differences.
302	Toad House block	Doesn't work	Garble graphics.
303	Ball 'n' Chain	Works
304	Spike Pillar - down	Works
305	Final Castle Create Loop	N/A	I have no idea how this works.
306	Final Castle Wrong Path	N/A	I have no idea how this works.
307	Spike Pillar - up	Works
308	Spike Pillar - left	Works
309	Spike Pillar - right	Works
310	Fog FG effect	Partial	Graphics are not loaded correctly
311	Snow FG effect 1	Works
312	Rise or lower while/once on Mushroom Platform lift - mechanical	Works
313	Snow FG effect 2	Works
314	Snow FG effect 3	Works
315	Cloud FG effect	Partial	Graphics are not loaded correctly
316	Water FG effect 1	Works
317	Water FG effect 2	Works
318	Fire FG effect 1	Works
319	Fire FG effect 2	Works
320	Fire FG effect 3	Works
321	Light FG Effect 1	N/A
322	Light FG Effect 2	Works
323	Squishy cloud platform	Works	Both players can interact with it at the same time
324	Grassland Clouds FG effect	Partial	Graphics are not loaded correctly
325	Small Grassland Clouds FG effect	Partial	Graphics are not loaded correctly

Modding 101 - Creating a Bare-Bones Level

Welcome to the world of New Super Mario Bros. DS modding. Making your first level is the first step every modder takes when starting from scratch.

In this tutorial, you'll learn how to:

Install the necessary tools to start modding
Open your ROM in the editor
Open a level from your ROM
Create a bare-bones level to build from

Section 1: Getting Ready

To edit the game, you'll need a copy of your New Super Mario Bros. DS ROM and the New Super Mario Bros. Editor (NSMBe).

We are not allowed to give a download to the ROM. If you have a 3DS, here is a guide that lets you dump your game cartridge ROM using a modded 3DS.

For the best compatibility for more complex tasks, you will need a US region ROM.

Head over to GitHub to download the latest version of NSMBe from the Mamamia Team. When you click the link, you will be taken to a page that looks like this:

Just click on NSMBeX.X.X.zip to download the editor. (The X's will match with whatever version the editor is on. As of writing this version is 5.4.1, as seen in the screenshot)

Now, in your downloads folder, you need to extract the zip file. On Windows, this is done by right-clicking the .zip and clicking Extract All... Just click extract on the window that appears. You should now have a folder in your Downloads folder named NSMBeX.X.X.

The final folder will look something like this:

You have now installed the necessary tools to begin modding

Section 2: Opening Your ROM

Now that you have the editor extracted, let's open up your ROM!

Inside of the NSMBeX.X.X folder, open the app named NSMBe5.exe. You should see a window that looks something like this:

Now, click on Open ROM... and open your dumped ROM of New Super Mario Bros. DS

The ROM will have an extension of .nds

You should now see this:

You have now opened your ROM in the editor

Section 3: Opening a Level

Now for the fun part, editing a level!

To start, we will open 1-1, Area 1. To do this, open the World 1 drop down, open the 1-1 dropdown, and finally double click on Area 1.

Each level in the game has a various number of Areas. Nintendo used these as a way to keep each sub-area separated. For example, Area 1 of 1-1 is where you start the level, and Area 2 is the bonus room found in Area 1.

You will now be presented with the level view:

If the level view appears too small, you may need to modify the config file. To do this: open the file named "NSMBe5.exe.config" using Notepad, delete the lines: <System.Windows.Forms.ApplicationConfigurationSection> <add key="DpiAwareness" value="PerMonitorV2"/></System.Windows.Forms.ApplicationConfigurationSection> After deleting the lines, save the file, restart the editor, and open Area 1 again.

You have now opened a level from your ROM

Section 4: Creating a Bare-Bones Level

It is best practice to start from a blank level, so let's clear out the existing level by pressing Ctrl+A to select everything in the level, followed by clicking the at the top of the editor window. Your blank level will look like this:

Now that we have a blank level, what do we need to add back?

All levels in NSMB DS must at minimum have a Start Entrance and at least one main View. With that being said, let's add them back!

To begin, we will add the main view. To do this, click on in the sub-menu bar. This will show a list of all the views in the level (or it would if we didn't just delete everything in the level). To create a view, all we need to do is click on Add. Your level will now have a transparent box:

You'll notice a bunch of settings here. For now, the only thing you need to worry about is checking Scroll vertically. This allows the in-game camera to follow Mario up and down inside of your level.

The View defines the bounds of your level. The camera is not allowed to go outside of the current view. Mario can go above the view, however the camera will not follow him. The sides of a view will stop Mario. Mario will die if he falls below the bottom of the view.

Click and drag the small box that says View 0 and move the View to the top left of the level. While we're moving the view, go ahead and grab the bottom right box and extend the view to be one square big. You're level should look like this now:

Now, let's create the Start Entrance. Click on the button in the sub-menu. Similarly to the views button, this will give a list of every Entrance that is in this level. Go ahead and click on Add to create a new Entrance.

Once again, there are a few settings on the entrance that you can play with but for now let's just move the entrance inside of our View.

There we go! We have what's at minimum required. However...if we were to play this level now, Mario would just fall down and die. Let's add a floor and the Goal Pole's Flag to this level!

To get to the Tile picker, click on the button (and also click on Tileset 1 if it is not already selected). Your side bar should now be filled with Tiles!

Go ahead and pick the tile I have selected (highlighted in red in the screenshot), then right-click to place the tile in our view. After this, you can grab the corner of the tile and stretch it out across the view.

Not bad! Now, let's make a Goal Pole for Mario to clear the level with.

First off, click on the button in the sub menu to bring up the Actor List.

This is every Actor in the game. You'll become familiar with more Actors as you begin making levels. For now, enter "Goal Pole's Flag" into the search box. This will now filter out all other Actors.

Click on the Actor in the list, then right click in the level like you did for the tile. This will add the Goal Pole's Flag into the level.

On the left, you'll notice that some options for the Goal Pole's Flag has appeared. All Actors will have an options menu appear for them when they are highlighted in the level.

All that's left to do now is finish tiling the Goal Pole.

Test your knowledge! The Goal Pole tiles are located in Tileset 0, try and build the flag like the next screenshot! Here's a tip, the Goal Pole is 9 tiles high and two tiles wide.

With the flag created, we now need to build the castle. To begin, head over to Tileset 2 and click on the castle. Now, right click to place the castle and drag it to create the castle. Your level will look like this now:

We're almost done. The castle in this game is composed of three tiles: the castle we just created, the wall that will stop Mario, and the roof that allows the small flag to show up after you cleared the level. Select the wall from the tile picker:

Drag this wall over the castle you created.

Lastly, drag the roof tile over the castle like you just did for the wall

You have now created a bare-bones level

You can now save your level using the save icon or by pressing Ctrl+S.