Firstly I'd recommend a held item similar to ever stone, but instead of preventing evolution it prevents experience gain as a whole. This would be useful to people who want to use a mon in the wild/safari and still be able to use it for a tournament. If you wanted you could enable EV gains but I'd understand if you didn't.
Secondly, nature rerolls. The name says it all.
Secondly, nature rerolls. The name says it all.