The entirety of this stage takes place on the back of General Snake, which is segmented, meaning there are gaps between the pieces, so be careful not to fall into those. Just go to the right and anytime you see the bomb symbol, use the bomb to be able to continue. Stand on the green thing to open up the vent, then toss a bomb inside to launch yourself upwards to some clouds, which can be used to get to the right.
Be careful of the poisonous spikes that come out when you slide down, where you'll find another switch/vent thing that launches you to some a long series of clouds. If you still have the Rat Head, you'll find the spot where you can use its action at the next switch/vent thing, which will net you the MUMMY HEAD. Keep going until you see a bomb symbol below some spikes, which will launch that section of Snake to allow you to bypass the spikes.
When you are blocked in by Snake's body on the left, you should see the Mummy Head icon flashing in the bottom left, so use its action to get to the bonus stage. After being transported to the next section, you should see the icon for using the Cedar Couple Head, so use it to get some extra Moonsparkles. Eventually, you'll come upon a seam cut where there is something in your path, you must jump it, as this will hurt you.
Sliding down Snake's body continuously will get you swallowed by him, where you'll meet up with General Rat once again. Pikarina decides to use him as a flotation device to get through Snake's body, which is set up as an auto- scrolling area. All you really need to do is jump over spikes and gaps until you get to the end, where you will go through a series of seam cuts, including the jumps, and get out of Snake's body. Hit Snake with Pikarina while he's down to get the SNAKE HEAD, then you will go through some QTEs to finish off Snake for good.
