Mega Mutant

Top
HP Def MDef XP TP Gold
6000 127 50 4000 150 5000

Vulnerabilities
Light Water Fire Shadow Tossable
100% 100% 100% 100% Yes
No Status Vulnerabilities
Bottom
HP Def MDef XP TP Gold
6000 127 50 0 0 0

Vulnerabilities
Light Water Fire Shadow Tossable
100% 100% 100% 100% Yes
No Status Vulnerabilities

Strategy

Mega Mutant will cast Obstacle for a random status effect, put characters to sleep, and throw shurikens for physical damage.

Unlike the other Mutants, Mega is vulnerable to physical damage as well as magic. You must defeat both parts, but neither changes their script when left without the other, so it's relatively safe to not defeat them at the same time.