Hint Defeating Bosses:
Note: This trick will work on levels 2, 4, 6 and 7. Toss a grenade at the Boss. Pause game play after the Boss begins to flash. The Boss will accumulate damage while the game is paused. A single grenade may be used kill the Boss with this technique.

To kill the Boss on level 5 easier, repeatedly throw grenades at him while he enters the screen.