This can be a difficult stage in any%, and a real run ender in both major categories. The armadillo skip can waste a lot of time if you miss it, less so in 100% (unless armadillo really wants to ruin your day by rolling). For the most part, the platforming between fights isn't tough, there's one hallway where you want to use particular positioning to manipulate enemy behavior, though, after the Mandrill fight.
Armadillo skip Edit
The armadillo fight can be skipped by bypassing the trigger locking the camera into place for the fight. If the camera stays low enough, armadillo just won't spawn, so you can just move on without fighting him. If you get the skip and the door opens, but you jump, the camera will scroll high enough to initiate the fight, but you don't have to fight him.
There are two ways to do the armadillo skip, there's a fast way and a slow way. Both of them open with killing the turtle with fire and swapping to ice. The slow way will get hit by one of the bullets to knock X into the right position, then fire the charged ice sled to the left which will shove you into the door. For a demo of the slow method, look at the start of the basic any% sigma 3 video.
The faster skip avoids taking the hit, instead you get into the right position before firing the charged ice to the right, then walking into position to get shoved by the sled. This version can be done as fast as you want, you can start charging before X even drops into the stage and just barely kill the turtle before gaining a full charge, or you can hold off on starting a charge if you aren't comfortable with the exact movements you need to make.
There's a visual cue you can use for where to position yourself when firing the ice. If you just let X drop into the stage and don't move at all, that position relative to the background objects (the bolts in the background) is about what you want, just on the objects near the door.
If you get a full charge before killing the turtle, but you dealt some damage to it, there is a backup you can try that's quicker than releasing a charge and starting over. Just switch to ice, bonk the turtle, then continue the skip as usual, the ice sled should kill the turtle without breaking.
After doing the Armadillo skip (or fighting Armadillo like you would in the first fight if you missed it), charge c.sting to get through the next room without taking hits or having any risk of drops. The Chameleon fight is exactly the same as the first.
The hallway before Mandrill can be done with c.sting as well, but other charged weapons can be used to kill the enemies in the hallway. Mandrill fight is also identical to the first one. After Mandrill, swap to spark and start charging. At the first drop, get very close to the wall (you can touch it or slide, but that just slows you down, it's the horizontal position that's important to get). This causes the first blowfish to try sucking you in while facing right. When you get to it, the fish will still be facing right, release the charged spark from point blank. You'll get pulled to the right a bit by the second fish as it dies, and the third fish will get killed as well. Jump over the lower fish and swap to rolling shield for the octopus fight, fight him exactly as you did in the first encounter. Charge up c.sting for the next section. If you need health, take the upper path which has a large health pack, otherwise take the lower path and try to keep from kicking up too many dust sprites, there's already enough lag without causing even more yourself. Mammoth fight is the same as the first.
D-Rex fight Edit
Open the fight with a dash shot, then use boomerangs. You can buffer a dash jump at the start of the fight by holding right, dash, and jump when D-Rex's health bar is done filling, then just press shoot shortly after your jump. You can sometimes bait chomps out of d-rex by standing on the lower half when the upper half is at the top of the room, it will drop to try to crush you, so just hop onto the lower half and get off asap. When D-rex goes to the right side and begins charging a fireball attack, you can get a couple hits in for free. It can be dodged really easily if you know the timing it fires, just dash underneath it. It can also be dodged by jumping over, but it will curve upward to hit you, so be careful.
Missing the armadillo skip is a little less brutal in 100%, since you can hadouken rather than fighting normally. The setup for the air hadouken requires a different movement up to Chameleon than any%, but for all of the other hallways, everything done in any% is what's done in 100%.
Air Hadouken Edit
After the armadillo skip, swap to fire, and when you reach the far wall, start charging while you jump. Use the fire to kill the two miners in the way and enter the boss door charged and swap to ice to set up the air hadouken.
To do the air hadouken, plant the ice sled partially in the wall so it doesn't fall down and stand on top of it. Then, input the quarter circle forward and pause the game. If you came in damaged for some reason, use a subtank here. From ice, the faster way to get to buster is pressing down twice, then left. Unpause, and either mash shoot, or wait until the game is close to fading back in and just hold shoot. The timing is pretty lenient on holding shoot, so it's easy to go with that.
If Chameleon opens by dropping spikes from the ceiling, you can get hit by a spike before being able to fire the hadouken, in which case just transition into the regular boomerang fight. Setting up another hadouken can be time consuming, and it isn't guaranteed to work by any means. Chameleon can also start going invisible and be unable to hit for long periods of time.
Mandrill Hadouken Edit
The Mandrill hadouken can be done a few ways. The consistent and easy way is to just shoot ice to the left wall, then fire a hadouken. The more difficult way is to fire a hadouken immediately when the fight starts, buffering the input to get a first-frame hadouken. If he jumps, it will miss, and if he launches sparks at you then you have a 4 frame window to jump out of the way (if you got the hadouken right).
Octopus Hadouken Edit
The Octopus hadouken is simple, just shoot an uncharged shot when the fight starts and it will destroy one of the torpedoes headed at you, then fire the hadouken to make Octopus land on it. Don't just autopilot the hadouken though, Octo can jump high or low, so if you fire early you might just miss. Look at how high he jumps first.
Mammoth Hadouken Edit
Just walk forward a few steps and hadouken to the left. He always opens with the same jump.
D-Rex Hadouken Edit
http://www.twitch.tv/domalix/c/4294980 Domalix's domdouken tutorial and demonstration.
The BBdouken/Domdouken is a simple, low risk quick kill on D-Rex, so there's no reason not to learn it (if you have the means to practice it). When D-Rex's health bar fills up, hold your dash button, this will get you a dash on the first frame of the fight which will carry you across the room. Toward the end of your dash, start a quarter circle forward, such that you end up hitting right after your dash ends. This pushes you flush with the bottom half of D-Rex, so a jump sets you right on top but not bonking into him. After completing the quarter circle forward, you have a relatively large window to press shoot and get a hadouken, so you use that window to jump on top of D-Rex and shoot when you land. Messing up this hadouken usually means shooting a lemon rather than a hadouken (pressed shoot too fast), in which case just do the old method and wait for the top half to drop back down and hadouken it when it tries.