In the 2nd stage of the Clocktower level, after the big fall, you should see a block with a card. Pull the block away and jump through the pipe. In the next part, keep up with Prunchau and a giant key will fall from the sky and increase the life bar to five gears and Tongara's key will be golden. Don't go into the box next to Tongara; pull a block out and jump on it. Next push another block through the wall and you will see a rocket. Lift the rocket and you will be transported to the boss.