Shrine of Forbidden Knowledge
Building • Cost: 3 • ATK: • HP: 5
Upkeep: Your base takes 1 damage.Draw/Discard phase: Card draw +1, hand size +1Your Demons are unstoppable by units.
Black • Demonology Tech II
"Card draw +1, hand size +1" means that instead of discarding your hand and drawing that many cards +2, capped at 5, you instead discard your hand and draw that many cards +3, capped at 6. — Sirlin
Having a detector (or a Tower add-on) doesn't help against the unstoppable keywords. Even then, unstoppable attackers can ignore patrollers. — Sirlin