Unlocks: Tree Rex’s “Woodpecker Pal” Ability
Later in the level, you’ll have to solve a block puzzle in the Under Mountain Mechanogear area. You’ll probably want to head over to the ledge and drop to the new area, but don’t do that quite yet.
Instead, push the middle block off that same ledge to the area below.
Now drop to the area below and push the box—which now carries the second box we pushed down here—into the empty slot in the walkway.
Head up the ramp and push the second box forward to fill the other hole in the walkway.
Now just follow the walkway around to find a Soul Gem.