Darker Side Guide:
Part 1:
When you enter you see a machine that spits out boulders and goombas, ignore it and jump up the platform behind it.
From that platform you can long jump over to the machine when it comes nearby. Two stomps will kill it and give you a life up heart.
While you’re getting used to the area, it’s a good idea to get, but I find it fairly unnecessary once you’re learning later stages.
Part 2:
The next part involves vertical poles you need to climb and cages you need to wall jump off, no real good advice for this, the challenge isn’t too bad.
The next section involves you swinging from a horizontal pole, to other poles that fall into the lava below periodically.
This ENTIRE part can be completely bypassed. On the last vertical pole, instead of riding it down, jump from it straight away and do a cap/dive jump, where you throw your cap, and then dive towards  for a bounce. Once you’ve bounced and gone a decent horizontal distance, dive again.
If you do this right, you’ll grab on to a stationary horizontal pole. From there, do another cap dive jump and you’ll land on the next section.
I found this to be a little harder to pull off at first, but also much faster and much more consistent. That’ll be important because Darker side is nothing if not long and much of the challenge is fighting your own impatience.
Part 3:
You’ll come to walls of different height travelling through the lava. This is the “Have you learned the triple jump?” challenge. Wait until a small wall is coming past, jump to it, then immediately jump to the next one along and then to the one after that. If you’re doing it right, you’ll jump to the small wall, double jump to the medium and then triple jump to the large wall.
Doing this right will completely trivialise the challenge, it also helps to get your camera directly behind you if you can.
Part 4:
The next part is an absolute bastard. It’s the place where I died most consistently because the fireballs handle like shit.
The first thing to note is that there are two health hearts in this area, don’t touch them unless you’re at 1 health. Beyond that there’s not much advice I can give, spin your fireball in a circle in the lava to gain momentum and jump between pits.
Part 5:
You’ll come to a maze of walls, with the aim being to use the possessed plant to push platforms up and make your way along.
There’s a heart hidden in the lava behind the structure, so if you’re low go and grab it.
Push up the first platform and jump up, then the second.
From here, zoom the camera out and you’ll see an area that you’re meant to get to on your right.
You could use the plant to do this by going up and around, or you could just ignore the plant, jump out of the structure and then cap jump to the area on the right.
Part 6:
You’ll get to a cave with ice water that comes from above and fuzzies along the bottom. Wait for the fuzzies to come around halfway towards you and jump towards them. The ice water /should/ come down from the ceiling and let you swim to safety.
Part 7:
Grab the Yoshi, start on the right hand side, wall jump to the left to dodge the fuzzies and then just don’t move. The Fuzzies that spawn above you can’t actually hit you if you don’t move. Drop Yoshi when you’re done, he’s just a disadvantage for the next section.
Part 8: Use the P switch to deploy flower road and just follow it along. The only thing you have to do here, is triple jump to get over the wall. When you come by the Sphynx, get off, answer his riddle and get your Heart Upgrade for a full heal and bonus health.
Part 9: The “Have you learned to wall jump” segment. Activate it with your hat and follow along. Two things to be careful of, sometimes you won’t grab onto a ledge and will need to double wall jump, don’t worry, just let it happen. The other is that the horizontal coin rings dictate where you’ll want to jump, there’s a trap at the end of this segment where if you stray too far to the left, you’ll get knocked off.
Part 10: Grab Glydon and fly to the hurricanes.
If you want to beat every segment, fly low and you’ll easily avoid any danger and get to the next segment.
If you want to bypass the last third of the level, go as high as you can and get as much height off the last hurricane as possible.
From there, shake the controller like a lunatic and you should just be able to fly all the way to the final area. (Part 15).
Part 11: Use the forks to flick yourself over, there’s nothing to this other than to be careful of letting go of forwards, because the forks will accidentally flick you back if you’re not careful.
Part 12: Go down a pipe and you’ll find a platform with a Pulse Beam on it. Do not touch it with Cappy under any circumstances.
Jump to the platform and it will start moving, Enemies will start spawning on platforms to your sides. Instead of remaining on your platform, jump to the enemy spawns and spam cap throws. This will lag the game, but you’ll be totally safe. As the platform goes past, just jump over to the next enemy spawn and repeat. I’ve been told you can also just hang off the edge of the platform for the same effect.
Part 13: When you get to the end you’ll find a woodpecker bird, possess it and jump up and grab onto the swinging wall. If you do not hit the wall right of centre, let go when it’s safe and try again.
Once you do, your aim is to flick yourself up when your wall hits the end of its arc and get to the next next one along.
Do this twice and you’ll hit an actual platform. Flick yourself up, being careful of the remaining swinging walls, since they can dislodge you.
Part 14: Donkey Kong: It’s a standard 2D stage except your controls are messed up, there’s no easy solution to this beyond to have a tonne of health and tank a bunch of inevitable damage from your controls being a garbage fire. When you get below DK, hit all the blocks beneath him to kill him and escape.
Part 15: Jump in the painting and enjoy your victory lap. It will take a miracle for this segment to break through 6 health points so just storm through and end the game.