There are several Spikes in this level. They throw giant spike balls onto the seesaws in front of them and into the lava. If you stand on the opposite side of the seesaw when a spike ball lands on it, you'll launch and stomp the Spike. Stand on the first seesaw and let the spike ball launch you. On the next seesaw, in the corner, let it tilt down towards the platform to reveal a hallway. Walk around and you'll find a plant with the first gem. Go past the spike ahead and drop down around the corner. Walk under the seesaw towards the Star and you'll find the second gem. Step on the nearby P-Switch to move the seesaw so you can cross under it to the other side. Climb up the ladder, being careful to avoid the spike ball. You'll find the third gem under the seesaw. Cross the seesaw to the right of it to reach the seesaw to the Star.
Special Challenge: Do not defeat the Spikes.
You'll have to use the ladders and have good timing to do this.