Jak II Vita

In Jak II for PS Vita, while exploring some ancient ruins on a forbidden island off the coast, Jak's best friend, Daxter, is knocked into a vat of Dark Eco--a terrifying and deadly substance that could corrupt the world forever--transforming him into a weasel-like rodent.
The village sage, Samos Hagai, tells Jak that there's only one person who holds the secrets to transforming Daxter back. Now the pair must set out on a quest in search of a wise old sage who has the power to restore Daxter to his former self.