Activate the eclipse.
You will learn from a radio near the PaP staircase, that Brock has lost his bag of dynamite. It is currently hanging from the crystal tower, near the minecart entrance. To get it down, you will firstly need to knife 4 particular gongs in a total of 8.
When a wrong gong is knifed, the crystals will glow red, if a correct gong is hit, nothing will glow.
They are located in the following places
Near Brock and Garry's brick prison, and the tunnel entrance
In the same area, in front of the tunnel entrance
On the left of the minecart entrance
Next to a wallbuy location, in the spawning room
Right on your left, when entering the mud maze from the spawning room
On your right, before leaving the mud maze
On the far right, after the mud maze, before the wooden bridge
Right on your right side after the wooden bridge
When all correct gongs are activated, the crystals will glow yellow.
To continue, you need the Fractalizer (The PaP-ed version of the 31-79 JGb 215). Shoot the crystal, the one which the dynamite is hanging from, the ray will bounce between crystals and eventually come back to drop the dynamite. Be careful, you need to catch the dynamite by standing bellow it when it falls, otherwise you will need to do this step again.