I think it would be a good idea to implement some kind of reverse rare candy that lowers a Pokemon's level by 1. It would be useful for getting a colored Pokemon that is unbase back to base or evolving a colored Pokemon then bringing it to base. Here is an Icon that I made just in case :D

Reverse Candy:
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I'll edit the pic if anyone suggests something good for me to change about it.

Well, the Rare Candy can lower a pokemons level by 1 too, only theres a 10% chance.

There is already an unofficial "Rotten Candy"
It's like Rich said.

yeah like other people said thats already happening but rare chanse

I have a lv4 pokemon in my box

That's pretty lame imo. Rare Candies should only raise level as they do in the video games. I did know about "rotten candies" but I don't like the fact that they can lower so I made this idea in hopes that gets removed and this get added :S