It's amusing but there aren't nearly enough variations to make it at all as fun as the usual Toribash. If it's going to be challenge based and 2D it'll have to play differently than usual. A match of toribash is dynamic and meant to allow you to position yourself in response to your opponent. That can't be done here by challenge makers because their moves are set: The only way to outdo the player is just to make your tori really, really big, so that regardless of what the player does, they can't escape the giant scissorlegs on your mod. Then the only way to fight the giant scissorlegs challenge is to create an equally big and destructive mod. Somewhere along the line, predicting what your opponent does, dodging, blocking and all that, disappears.
Ahem. I think there are two problems: big mods in a small room, and an imbalance between the challenge and the challenger. If Minibash is to play like Toribash, it needs to have two players to react to eachother, not have your opponent fall over and repeatedly slam his face on the ground. Otherwise it will have to be a lot different.