Tartarus, the endless Abyss

Indestructible
During your own turn, you may tap swamps your opponents controll to add mana to your manapool.
{2}{b}{t}: untap all swamps. Until end of turn all
swamps on the battlefield become 3/3 black elemental creatures. Put three +1/+1 on all
swamps you controll.
Partner with Gaia, Mother Earth