This card is currently the second least played Uncommon at 0.45, so I think it's another one that could use some sort of buff.
For specific ideas: it could copy the same things Master of the Past looks at and do those things (or a significant fraction of them) to the opponent, it could directly copy the effect of the opponent's last played card without having to spend another turn on that card, it could become Quick serving the same purpose.
Although, the best property to add would be one that counteracts the fact that it's even more unreliable than normal Illusion*; you have very low odds of your opponent playing a card you want to play while you have Mirror Strike in hand, you might have to hold onto it for a long time before getting an opportunity, and many of the cards you might want to copy might also prevent you from doing so (whether by discard, resource reduction, or making you lose the game).
*How Illusion can't help you if your opponent doesn't have any cards that will help you if you play them.