Collapsing Tunnels

{t}, pay 1 life: Add {1} to your mana pool.
{t},{b}{g}, sacrifice Collapsing Tunnels: Destroy target creature with toughness 3 or less.
Mulch (When this permanent enters your graveyard from the battlefield, you may pay {b/g}. If you do, exile it, pay 1 life, and search your library for a basic land card and put it onto the battlefield tapped.)