The Extra Bit is a flag that can be used to give a sprite different behaviours without having to insert two nearly-identical copies of its code. Click to enter sprite editing mode and press Insert (alternatively Edit > Insert Manual...) - the field Extra Bits (0 - 3) determines how the sprite is inserted:
0 - regular sprite, extra bit clear
1 - regular sprite, extra bit set
2 - custom sprite, extra bit clear
3 - custom sprite, extra bit set
A custom sprite will generally note in the .asm file or a readme what effect setting the extra bit will have (if any). Regular sprites are not coded to use the extra bit and will disappear in-game if set. The only exception is the Goal Tape sprite, whose extra bit is handled by Lunar Magic.
What are extra bytes?
Extra Bytes are a means of assigning extra data to any one sprite inserted in a level, for much the same reason as extra bits above. Click to enter sprite editing mode and press Insert - the field Extension (00 - FFx) is used to assign the extra byte data. A custom sprite will generally note how many extra bytes it uses and their related effects in the .asm file or a readme. This feature is not used in regular sprites.
Beware! Swapping the numbers of custom sprites that use a different number of extra bytes will cause sprite data to be misread, very likely leading to a crash. This only applies to reinserting sprites into the ROM with PIXI; changing around the sprites placed in a level is safe.
How do I change what a sprite looks like?
Change the sprite's code to use different tiles. For changing the appearance of a vanilla sprite, you can also try STEAR.
Why don't my sprites look right in Lunar Magic?
Go to and press Ctrl + Shift + Page Down. You can edit the display Map16 of the sprites, and press F9 to save them. You can also use SpriteTIP if you just want custom sprites to appear normally in Lunar Magic.