From a power standpoint, it's a really effective way to swing a table, and if you're ahead too it can backfire if you just decide to slam it willy-nilly
The idea of copying opponent's creatures is somewhat interesting, but it places you at the mercy of what the opponent has for you to take any value out of this
Allowing a payment any number of times is asking for combo potential, and in the color with Cabal Coffers and all the sacrifice outlets you could want, the upper bound of Adversary seems quite strong
Otherwise, you will have cards you will not want to discard, and this effect will go unused
When this happens, the next turn player automatically becomes the commander (unless a different player killed them with combat damage, in which case the monarch moves the same way it normally would)
This means that playing Ojutai can lead to a complete shutdown of your opponent's combat steps if you have a couple of Dragons on the battlefield