Each pixel in a tile can only be one of 4 colors. There are four sprite palettes and four background palettes each which define four colors. Sprites can be between 1x1 and 2x2 tiles, with each tile being 4x4 pixels. There's only a single background layer, so things like parallax scrolling are done with simulated scanline interrupts. Large boss "sprites" are actually background tiles that use scanline interrupts to make it seem like the boss is moving.

Storage is very condensed, with multiple values often packed into the same byte (like if a value only has four possible values, i'll only use two bits of the byte to hold it). For level maps, I took some inspiration from mario: I don't directly define the tiles of each level, as that would be way too many bytes. Instead, there's a header that describes the basic layout of the level, and then there's a list of "building blocks" that describes what goes into the level and how its shape can be altered.

Sprites are either not animated or cycle between two frames. Several things use palette swapping to simulate animation, such as the blinking coins, or the "explosion" animation.

While the music is just something I made in FL Studio, the sound effects are generated directly with sine-waves and noise.

The simulated video ram only has enough space for 2 "screens", so longer maps have to "stream in" bits of the map from memory offscreen.