Reptile Metabolism is an upgrade for Guapo, Juan's crocodile Amigo. When Guapo revives himself he comes back with 90% of his health, so he is ready to fight again right away.
Normally a revived Guapo comes back weak. With this upgrade he returns at nearly full health and can keep attacking.
Let Guapo kill 50 enemies. Command him to attack targets to speed this up.
Yes. It makes the self-revive far more useful in long outpost fights.