>>38775064All they need to do is make it a perfect replica. Like you batter a Ferrothorn down to 30% and burn it and then it's switched out. Currently, when the Zoroark comes in, you see a mysteriously full health Ferro and immediately know you're looking at a Zoroark, but it should instead show replica of the Ferro, right down to a completely fake fuctionless Burn status that you would only figure out once it started doing Zoroark moves or the Burn damage doesn't happen at the end of the turn.
It also needs to not break, even after fainting so you can never quite be sure if you've KO'd the Zoroark if played right. Did you just KO Greninja there and are ready to set up and go nuts or is the real Greninja fine and just waiting for a chance to Battle Bond?
The mindgames that could be played with a perfect Illusion is worth more than the subpar Pokémon you'd have to drag along to use it.