See Challenge # 110.

Whoa. That's a very painful effect. It won't always kill something, but a lot of the time it will, and it could lead to players manascrewing themselves by holding back lands until you tap out. I fear is very cheap for this effect, even as a colour-specific hoser.

It's a tricky little ability, because I could see people forgetting that it's there. Then out of the blue, play a land, and tap my three Assassin's Outposts to -3/-3 to the creature you just played.

­Archer's Outpost has that problem, too, but at least the ability is effecting life totals, and not the state of the board. Sucks to lose to a land out of nowhere, but it seems more forgivable to me for some reason.

Hmm... maybe deathtouch at sorcery speed? You probably have better ideas in your head than I have in mine, Link.

I realize that this is too powerful, but I was really stuck for things to do for the black land. Discard seems way to powerful, especially if you get this online early. I was going to have it exile cards from graveyards, but that seemed too weak and like it didn't really hose green/white. Basically everything I can think of for black is too powerful early and too weak late, or just too powerful in general, or just too weak in general.
Would "You may put target creature card from your graveyard on top of your library" be ridiculous?

­Volrath's Stronghold let you do it for 2-and-tap, without needing the enemy-landfall trigger. So bizarrely, no, it'd probably be fine. (More suited to rare than uncommon though.)

­Haunted Crossroads was uncommon. But we're both talking about some pretty old cards...