Really appreciate the feedback! I too dislike how the Necro Deck turned out to be a guessing game, I should've explained this in-game better. But it works as following:
1. It will "Reverse" every "Attack" or "Tallying" (4x card) you place (so you do harm to yourself instead).
2. When you place "Reverse", it will put an "Attack", so you can damage the boss (this card is their weakness).
3. Otherwise they will try to "Regenerate".