Pig Bang 1-21 is the 21st level of Pig Bang.
It's looked hard but it's not hard. If you destroyed the main tower, it's not the problem.
The best strategy for Pig Bang level 1-21 is to launch the Lazer Bird above the main tower. When it is directly above the tower, redirect the bird through the horizontal wooden blocks between the stone pillars. The bird should pop the pig at the bottom and the tower should fall to the right.