This boss will walk back and forth, occasionally spawning a projectile. Depending on the extra bit, it will behave like a custom Lemmy or a custom Wendy. By default, it takes 5 hits to kill. It can activate a switch in the middle of the fight.
Lemmy will either spawn a ball which will break on hitting a wall, or a ball which can be picked up and thrown at him to damage him.
Wendy will either spawn rings which will disappear on hitting a wall, or a rideable egg which can be picked up and thrown at her to damage her.
Make sure to specify the sprite numbers of the balls, the ring, and the egg in lemmy_wendy.asm! Check the ASM files for customization options.