What about the official anime and manga? Not as an item but as a thing. In the anime Slowbro and Slowking did it, and in the manga it happened with Red's Eevee. In PRO when you are doing the Hoopa Dungeon, your Pokemon are deevolved as well. Since I am suggesting for the item to be untradeable, it does not affect if you are poor or rich. 250 PvE/PVP are not a small amount but are also not a huge number, so you have to be careful and have an option to "pay" for your mistakes. It is similar price of how much a reroll would cost. Since it won't be tradeable, it will not affect the marcet. If anything, it will be a money sink. If what's done is done, why do we have a Mysterious Candy and a way to evolve level 100 Pokemon? Similar to how the Ranger Team was introduced to fuse forms. Few years ago saying that something like that to be implement would sound crazy and people would be against the idea, but time changes and it happened.