: Add to your mana pool. Put a -1/-1 counter on Devoted Druid: Untap Devoted Druid.
"Mana lurks in all things, even in the depths of one's own heart."
Official Rulings for Devoted Druid
5/1/2008 : You put the -1/-1 counter on Devoted Druid as a cost. That means it happens when you activate the ability, not when it resolves. If paying the cost causes the creature to have 0 toughness, it's put into the graveyard before you can untap it and before you can even pay the cost again.