The Fryguy boss from Super Mario Bros. 2. It flies around the room with an infinity sign trajectory, occasionally throwing a fireball, which disappears on hitting the ground. The player can hurt the boss with thrown items or with star power. After 3 (default) hits, it splits into Mini-Fryguys, which can be defeated with a thrown item or star power. The level ends after defeating all of them.
If the extra bit is set, hard mode is enabled. The boss will move significantly faster and throw more fire. The Mini-Fryguys will also leave behind Hopping Flame trails.
Check the ASM file for customization options, especially if you're using AddmusicK.
The best recreation of the boss out of all three that exist (the previous two have already been removed). Originally a C3 submission by Sonikku, submitted with his permission.
Converted to PIXI and added SA-1 compatibility. Added screenshots and tags. I fixed two issues in the original sprite. One was the faulty check for star power which let you sometimes hurt the boss by spin-jumping on it (and by killing yourself on it). The second, more obscure one involved fireballs getting a glitched tile because of uncleared extended sprite tables.
(also 8 FPS GIFs because I couldn't get them below 1 MB in any other way)
Edit: Upon further inspection, the glitched fireballs were caused by Sonikku's Reznor Fireball Fix patch which I had installed in the testing ROM. The fix for the issue, however, still remains, as it is small (two instructions), useful for those who do use the patch, and ensures compatibility with other resources, too.