Solution to the hidden Bomberman-style puzzle in Zeppelin Castle Stage 4. The reward is just a 1-up and a Cross Tank, but it's useful to know.
Finding the Puzzle
The puzzle is in Zeppelin Castle Stage 4, on the upper route.
At the end of a long hallway, you'll see a wall you can easily get on top of and a ladder going down; go over the wall instead of down the ladder. (Sorry, neglected to screenshot this, will amend later.)
Slide though the passage at the top, land here, and place a Zornesbomb. Make sure you place it on the right side of the platform, not the left; if you put it on the left, you may destroy blocks that make the puzzle unsolveable.
This will destroy the block you're on and you'll fall down one. Repeat. Again, make sure to put it on the right.
This will create a passage to your left. Place a bomb to your left, and quickly (but not so quickly you screw up) slide into it to kick it into the hole. Turn around and slide out of the hole without falling down (you won't be able to get back up if you do.)
Repeat. This will blow out the first column of blocks, letting you drop down and collect the items. There is no solution to this puzzle as Grolla. She can come to this room, but she can't get the items.