Rock-Slide Rumble

Rock-Slide Rumble is the thirteenth level Crash Twinsanity, and is also the first stage in the 10th Dimension and the second Humiliskate level.

Description
The main objective is to rescue Nina Cortex from Evil Crash, who is using her as a sled down the mountainside, similar to how Crash uses Cortex as a snowboard. The Evil Crash plot is continued in Twinsanity Island and Bandicoot Pursuit.

Gems
Green gem: This first gem is right near the beginning of the level, inside the ants' structure.

Blue gem: Not long after the green gem, there is a section with many different slopes. You must slide up the left wall a bit to get enough airtime to make it to the left slope, then collect the gem sitting there.

Yellow gem: Not long after the first checkpoint, there's a hole to the right, barricaded with a wall of nitro crates. Slide up the right wall a bit to get over the nitros, then slide through the tunnel, collecting the gem on the way through.

Red gem: A little while after the first grinding rail, there's a hole to the right, similarly to the yellow gem. Slide up the wall a bit to get over the TNTs blocking the way and collect the gem as you slide through the tunnel.

Purple gem: Pretty much immediately after you leave the tunnel from the red gem, you must grind on the ridge in the middle of the path. The purple gem rests along the top.

Clear gem: After the purple gem, the clear gem is in a tunnel on the right, just like the yellow and red gems. Slide up the wall a bit to clear the TNTs and slide through the tunnel, grabbing the gem on the way through.

Trivia

 * This is one of many skippable levels in the game.