After single firing across the first room and into part of the second, put the Kapar enemy in your mouth. Note that if you're standing on the left half of the block, you'll swallow it with the enemy, causing you to fall in the water. Afterwards, jump over to the Blowfish in the water and combine for the ninja star powerup. I like to do one big jump and one small jump to get closer to the Blowfish, but far enough so he doesn't explode.
Take the water jet up to the entrance into the mountain at the top of the screen. While standing on the plank I like to turn around twice to make sure I still have my running speed. Instead of jumping twice, you'll sometimes be in a position to ledge grab, which I think is a little bit faster. Once inside, move to the left and use the powerup to get Shard 1. Like in 2-1, I like to slide into the wall to quickly change directions. Slide into the block and immediately take your powerup out. For some reason, it'll go into your mouth as you step on the trigger. After exiting, spit out the powerup, inhale the Cairn enemy, and walk into the cutscene trigger.
The next room is somewhat risky, because missing the powerup means restarting the level. With the Cairn enemy in your mouth, jump and spit it at the first Fishbone for the animal statues powerup. Float up and jump into the hole. The miniboss takes four hits, and since a large area around it collapses once it's killed, it's easy to get stuck in statue form while the floor collapses. The best real-time strat for killing this Kapar miniboss is to get one hit by bonking into it with the powerup, two hits by entering the powerup, and one hit by breaking out of it. Due to the invincibility frames, you have to delay the last hit a little bit. A safer strat involves going on the left side of the miniboss, where the floor doesn't collapse (right). Afterwards, grab Shard 2 and fall through.
The next shard is one of the more annoying RNG segments in the run. After breaking the block, you need to keep trying the powerup until you get Rick. To climb, hold left against the wall and press A at a certain rhythm (i.e. it's not mashing). After climbing to the top and collecting Shard 3, drop down and break out of the powerup to avoid faceplanting. My visual cue is to press B when Kirby lines up with the second wooden platform visible on the right.
Afterwards, go to the right and float up, using the collapsing platforms to jump off of. For some reason, the ones on the right collapse almost immediately, while the ones on the left take about a second to fall. Once you get past these platforms, float past the last enemy and fall towards the exit. Keep the powerup, because it's useful for the next level.