Baltasar was offered millions of gold by an anonymous monster to kill Sambacadabra. Like the professional assassin he is, Baltasar took the gold and asked no questions. When he found the witch, Baltasar started his attack and felt victory in his grasp until Sambacadabra suddenly cast a Mambo Jambo dazing spell. She quickly escaped the distracted assassin, taking a sample of his Cells with her. 
She knew that she had been very lucky to escape from a monster like Baltasar and that if he came back, she wouldn’t be so lucky again. That is why she mixed the Cells she had stolen from him with some of her own to create Petro Loa — a vigorous monster that would protect her from Baltasar in a future attack. The problem was that Sambacadabra’s masterplan creation is not what she expected: Petro Loa is a violent and unpredictable creature. He can definitely put up a fight against Baltasar, but Sambacadabra should also keep her distance from him, since he can’t distinguish between friend and foe. Petro Loa will assault anyone who comes too close.
In battle, Petro Loa is a very heavy attacker with high damage skills who can Poison his enemies and make them Bleed. He can heal himself and lose his negative status effects in one move, as well as gain Double Damage and Precision in another move, so you could say that he takes good care of himself!