Cannonball!: Do a cannonball from the diving board
When you reach the pool section of the track, stop on the diving board then bailout.
Hold the left trigger to get into the cannonball pose before you land in the pool below.
Pyromaniac: Finish the track whilst on fire
Reverse into the flame at the start of the track to set yourself on fire, then complete a faultless run without hitting any water. Also, don't slow down for too long or your bike falls apart.
The hardest part is clearing the initial jump over the first pool of water--try to drop off the first ledge into a wheelie then accelerate and bunny hop over the pool, then bunny hop again from the ramp to reach the roof of the hut. As long as you don't slow down too much and destroy your bike, the rest of the track should be plain sailing in comparison.
Waterproofing Test: Introduce electricity to water and get yourself electrocuted
Near the end of the track, jump onto the plane engine hanging from vines then stop and wait.
After a few seconds the engine will lower into the water and you'll be zapped.
Shocking!: Get stuck by lightning
Bailout at the top of the final rocky slope, launching yourself over the finish line and onto the roof near the lightning rod.
If you land in the right place, the camera will begin to pull back--wait a few seconds and lightning will strike.