And game mechanic you can make use of especially in situation where your initiative loses out to the opponent is to decide when to cast your mystery.
For example, his move 1 is Sage Naruto, and you will lose to his Sage Naruto in terms of initiative in Round 2. What you can do is Acupuncture him in Round 1 after he has made his normal standard attack move. I normally do it after his standard attack cause I don't understand sometimes how the debuff is cleared at the end of each round. But acupuncturing him after his standard in Round 1, I know he's mystery is locked in Round 2.
Then in Round 2, he can't cast his mystery, I'll let him make his standard move again, THEN I'll mystery him with my own Sage Naruto which has a chase with Mei & Fire Main to immobile & blind him after his standard in Round 2 lasting into Round 3, locking his Mystery again.
Not sure if my scenario explained was clear, but remember to play smart. There's power play, there's smart play, and ideally power and smart play will be optimal, but if you're f2p, you often have to rely on smart play to win p2w players (well, at least against those p2w who aren't very into smart play).