Giga Mutant can inflict Sleep. It does lightning and fire damage, as well as a powerful poison AoE. The Top counters every attack with MP drain - but only magical damage will harm the Mutant, so be ready with MP restoration. The counterattack will always hit the character who initiated the attack, so in the case of Double Techs, you can control who takes the extra MP damage. When the Top is killed, the Bottom will spam the poison AoE, so it is wise to defeat both parts at the same time if possible (when Boss Randomization is on, both halves of the mutant may roll different HP values, so be cautious).