Inverter feels annoying to play against, I would make it either shuffle the shells in the gun (maybe a new item for that) or allow you to choose one of the upcoming shells in the tube instead of the one in the chamber. You wouldn't be able to use it if there is less than 1 left.
I have found that items that guarantee damage in multiplayer creates a huge unbalance of fun between the person getting the guaranteed damage and the person receiving it. The person who uses the item feels a little better but the guy who gets shot always gets mad. I find the game more fun when the main RNG getting you damage is the order of shells in the gun and not the items that are distributed to players because often some player gets incredibly unlucky.