I think a rare enemy that drops rare loot should be Gabriella. But instead of killing her, you have to use a healing type spell on her. Then she'll either leave to bathe, give you a pickle, or laugh at you, all resulting in rare items.
Boss: Missing No.
Hp: 47930 (shows up as undefined on player screen.)
Weakness: Unknown
Attack:30
Defence:90
Description: A series of pixels
Bestiray description: Legend has it that seeing it causes your game to freeze.
Attacks:
Pixel swarm:- engulfs you with pixels
Basic attack.
1 does 2-30 damage
2 does 15 damage.
Skip adding stats, damage values, etc because no one really knows how exactly the final battle system will work. Giving a name and a detailed description will do just fine.
EPIC BOSS: a mixture of Mystical Zoey, Chuck Norries, and Bill Cosby. Stats: Health: EPICNEZ Defence: ∞ Damage: 99999999999999999999999. Weapon: A mouth that eats n00bs.