As an additional cost to cast Goblin Grenade, sacrifice a Goblin.
Goblin Grenade deals 5 damage to target creature or player.
10/4/2004 You can’t sacrifice more than one Goblin to get a greater effect.
9/22/2011 Players can only respond once Goblin Grenade has been cast and all its costs have been paid. No one can try and destroy the Goblin to prevent you from casting Goblin Grenade.
9/22/2011 The Goblin you sacrifice to cast Goblin Grenade doesn’t have to be a creature. For example, you could sacrifice Boggart Shenanigans (a tribal enchantment with the subtype Goblin).