Find this puzzle at ground level in the Hydra Empire
Start by pushing the green-edged block into place.
This lowers some obstacles, so you can now push the red block into place, on the gray square near the yellow block.
Push the yellow block as far as it can go, then return to the green block. You'll notice there's now a gray square open in the opposite corner from the yellow brick. Push the green brick to this new open spot (you will have to take the long way round, but there is an open path).
Now you can slide the yellow brick to the gray square that green used to be in. This completes the puzzle and grants a brick.