It's a custom Mario editor! Keys: 0 - Toggle Entering Level Editor Mode and Playing level In level editor: 1 - wooden blocks and pipe 2 - Gold block, (one) wood block, mystery block, bush, cloud, zigzag black level end, black level end block 3 - blue jump-through blocks, orange jump-through blocks 4 - coin, Mario spawn point 5 - Grass/Hills 9 - Goomba, Life Mushroom, Superstar, End Box, Piranha Plant, Koopa Toggling Keys: e - eyedropper: pressing e while in the level hovering over a block of your choice, automatically switches chosen brush to selected tile l - load level: pop-up menu when l pressed appears, select which level you want to load. (remember to save before loading!) r - reset level: when r pressed, you will be asked to reset level. clears all the tiles in level and asks for your chosen level width and height. q - toggling auto-arranging tiles setting: when q pressed (already selected when green flag clicked), it will auto-arrange tiles to form a structure without you having to go through all of the similar blocks 'till you find your desired block. space (hold) - while holding space and making a structure with auto-arranging tiles enabled, it puts your block in front of a structure you are trying to overlap without blending the structure you are building with the other structure. Useful for layering.
Griffpatch tutorial