Grenade Part 1 - General Tips
The sets of exploding boxes in this stage come in 2 colors. A set of continuous colors will explode if one explodes, and stop at the other color's boxes. Any level of charge shot (half or full) will "pierce" a box, destroying all boxes in its line of fire (this is most obvious at the early giant wall of boxes).
Remember the Mega Ball can be carried in front of Mega Man, letting you charge the buster while killing an enemy with the ball.
Always Be Sliding.
You should save at least 12 Mega Balls for the mid-boss, Ururunn. (The giant floating trash eye).