If you have two non-Hydra creatures with Wildwood Scourge's ability (perhaps because they were mutated using the Ikoria: Lair of Behemoths mutate ability), putting a +1/+1 counter on any non-Hydra creature you control will cause the two abilities to trigger each other indefinitely
While not exactly a card draw, it does give you access to more cards than are in your hand
This means they don't have to attack at all, but it still demands they are tapped and it forces your opponent to tap them on their turn
You can unlock that door even if there would be insufficient legal targets for that triggered ability
There are plenty of other playables worth mentioning, but I found that cards like Teferi's Protection, Swords to Plowshares, and Ephemerate are so unbelievably good at doing what they do that the third or fourth next best option isnt really even worth mentioning
This is nice, but its overpriced