Here’s the workaround
A recent patch for the excellent 2D action-adventure title Guacamelee! has regrettably led to a game-breaking problem for players who load up a save file after earning Pollo Power. If you’re in a playthrough after that point, you will be permanently stuck in chicken mode upon transforming. As much as I adore being a chicken in the game, that’s no good.
Once the issue was found, the patch was understandably pulled. The current workaround, as described by DrinkBox Studios, is to delete Guacamelee! and redownload it on PlayStation 3. For Vita players, the studio advises performing a cloud save via the in-game options menu and then doing the same delete/redownload process for an unpatched version of the game.
The real bummer here is that new downloadable costumes including the ones above have been indefinitely pushed back since they require the aforementioned (working) patch.