My opponent attacks with a 3/3. I block with my 1/1 Llanowar Elves, and have all of my land tapped from my last turn. Can I now tap my Llanowar Elves after it has been declared as a blocker to play Giant Growth on it, make it 4/4 until end of turn, and destroy my opponent's attacking creature when damage is dealt?
One thing to note: once a creature is blocked, it remains blocked even if the blocker is removed before damage is dealt. This works great against lifelinkers, since they deal no damage to a creature that is no longer there. It works less well on tramplers, since they just deal all their damage to the player instead.