Hi,
I have bought this engine years ago and I'm so far ok. But I wonder if I can use larger sprites and rooms to give a more 16-bit feeling instead of 8 bit by keeping every other gameplay aspect intact. Is there a simple way to achieve larger sprites, rooms, etc?
All you should need to do is make the sprites bigger and edit player_free (Gameplay --> Player --> Collision Checking) to use the new sizes. The enemy counterpart uses a variable hitbox size so it should adapt automatically (if you make sure the hitbox variables are set based on the sprite size in their create event, like with all the existing enemies).
You might need to tweak movement speeds and such (defined in init_character_maria) to make the objects move at a speed that feels right for the bigger sprites too, but that's more of a "feel" thing than something absolutely necessary for it to function.
Another alternative approach that messes with gameplay even less is to edit the draw code for every object and make them draw larger sprites as x*2, y*2, but still use the 16x16 grid for collisions in reality. (Autotiled objects would create larger tiles at x2'd coordinates as well). Could get a bit messy to set up, but would let you use larger sprites without having to compensate for larger sprites gameplaywise.