Boneyard Scourge
Oracle Text
Flying
Whenever a Dragon you control dies while Boneyard Scourge is in your graveyard, you may pay
. If you do, return Boneyard Scourge from your graveyard to the battlefield.Card Rulings
8/25/2017 If Boneyard Scourge dies at the same time as another Dragon you control, its ability won’t trigger.
8/25/2017 If Boneyard Scourge leaves your graveyard before its triggered ability resolves, it won’t be returned to the battlefield.
I'm pretty sure there's an Infinite Combo here somewhere, but I tired of trying to find it.
Ashnod's Altar + Bog Initiate + Black Market = Infinite Mana for the rest of the game. Yes, this combo is terrible.