Buy @ TCGplayer
If you control a commander, you may cast this spell without paying its mana cost.
Creatures you control gain indestructible until end of turn.
It doesn't matter whose commander you control. Any one will do. If you have two commanders, you just need to control one of them.
Once you begin casting this spell, players can't take any other actions until you're done casting it. Notably, they can't try to remove the commander you control to make you pay its cost.
