Thread:ShellBullet/@comment-2234004-20140203074043/@comment-11454852-20140206142642

Not really, you can cast it at any time because it doesn't state "when your opponent has 3 or less life". Drill Bunker can also be a finisher when the opponent has 4 damage and a center monster, but its not restricted to just using it then. I often cast Drill Bunker more than once actually.