Pitiless Plunderer
Oracle Text
Whenever another creature you control dies, create a colorless Treasure artifact token with "
, Sacrifice this artifact: Add one mana of any color."Card Rulings
1/19/2018 If another creature you control dies at the same time as Pitiless Plunderer does, you’ll get a Treasure.
If you use some sort of glorious anthem ability you get infinite mana.
Or if you have a blood artist you could kill them outright.