Pongify reads: 'Destroy target creature. It can't be regenerated. Its controller creates a 3/3 green Ape creature token.' There is no restriction on who controls the target creature, so you may legally target any creature — including one you control yourself.
When Pongify resolves, the targeted creature is destroyed and cannot be regenerated (CR 701.15 covers destruction; the 'can't be regenerated' clause simply means regeneration replacement effects won't apply). Its controller — which in this case is you — then creates a 3/3 green Ape token (CR 111.2).
This is sometimes done intentionally. For example, you might sacrifice a 1/1 creature that is about to die anyway, using Pongify to 'upgrade' it into a 3/3 Ape token. The trade is strictly a net positive in power and toughness.
One concrete example: You control a Llanowar Elves (1/1) that an opponent has targeted with a lethal spell. In response, you cast Pongify on your own Llanowar Elves. The Elves are destroyed, you get a 3/3 Ape, and when the opponent's spell resolves it has no legal target and is countered by the game rules (CR 608.2b).
There are no special timing or targeting restrictions beyond the standard ones (CR 601.2c): the creature must be on the battlefield and targetable (not hexproof or shroud relative to you). Since hexproof only protects from opponents' spells and abilities, your own hexproof creature can still be targeted by your own Pongify.
Unofficial fan resource — not affiliated with or endorsed by Wizards of the Coast. Answers are AI-generated estimates grounded in the Comprehensive Rules and are not a substitute for an official judge. Verify anything match-critical.