Definitely a breather level, very straightforward with no difficult part to it. The mine carts do all the work for you, and with spark, Armadillo is a pushover. The boss fight is the worst part of the stage, and it's only bad because you can get bad luck and have him roll a lot of times.
any%[]
Armadillo basic stage
You can (potentially) reduce lag by killing the first couple sets of bats, but if more than a few drops show up, it's probably causing more lag than you're trying to reduce. Doesn't hurt to try to kill a couple though, just shoot a few times when you get onto the cart, then after the first bend in the track shoot a few more.
Hold a charge and after the cart kills the flamingo near the pits, dash jump off, release your charged shot to kill the bats on the ceiling (and carry on through to the next flamingo) and fire a couple lemons. Right after landing, dash jump again and fire to kill the flamingo. It isn't too difficult to do smoothly, but releasing the dpad for a moment as you kill the flamingo costs very little and guarantees you won't just bonk into it. Before the first drop, there's a pillar in the foreground, if you jump there, it's fairly easy to barely get by the edge without touching it so you're at maximum falling speed sooner. If you do that jump by the pillar, though, you'll want to shoot the bat on the ceiling before dropping down to the platform leading into the bigger drop.
There's an optional jump that can save a few frames in the next hallway. There's a ledge you have to climb up to, and it takes one wallkick no matter what you do, so if you do a (somewhat) short jump and go off the left wall asap you can reach the right side slightly faster than going all the way to the right and doing a wallkick off the right wall.
The drop with all the mets and bats you have a couple options, you can jump off a ledge early on and clear every intermediate platform, skipping all the mets, which will save a couple dash inputs. You can also just dash off every ledge and nothing will hit you, both versions are safe and both are easy, so do whichever you prefer. Be more careful with the next section with the wheel enemies, it can be a little laggy if you cause a lot of dust sprites from dashing. It's not a huge loss but more careful movement can save you a small amount of time for free.
Fatso's bat jump
On the left: fatso's bat jump On the right: the traditional method of getting to the cart
After all the wheels is a one wallkick climb leading into the next mine cart section. Most common strategy is to do a wallkick (with no dash) to get on top, then dash across the short platform and jump to the cart. This causes some lag, so it can be better to wallkick up, dash jump to land in front of the cart then do a very small dash jump to barely get onto the edge of the cart. It's a bit more tricky to do properly, but once again, saving frames from lag is always nice. The best way through, though, is doing the fatso bat jump. If done from the right spot, a dash jump will not force you to bonk into the bat, so you can smoothly get in front of the cart.
Once on the cart, just ride it along until it crashes into the final miner, then dash jump off. Ideally, you land right on the edge before the big drop and simply dash off. This gives you the longest time with the fastest speed without forcing you to the far right of the screen during the drop. At dash speed it's possible to slip in front of the tunnel borer without hitting the front which is instant-kill, and it isn't too tricky to do. Alternatively, you can just slide down the wall right above him and continue holding right, you'll also land out in front of him unharmed. There's nothing really in the way until the final mine cart, so just dash on over to it.
Birdless
Preventing all birds from spawning
When you get on the final cart, after the cart hits the first level point by the first miner you encounter, fire 2 uncharged shots. These will kill the bats along the ceiling so you dont have to bonk them or do some fancy dashes underneath them. After the bats is the section where all the birds spawn. With the right movements you can avoid spawning all of them, which saves a good deal on lag, and it's very simple, so there is no reason to not learn it. When the cart gets past the narrow area with the spiked pits, the first two enemies are miners. Jump when the cart is halfway between the first two, and continue jumping each time you land. Do 4 full height jumps this way. During this process, X naturally drifts to the right, so tap left a little bit during (or between) each jump to avoid falling off the front. After the fourth jump, wait a moment before jumping again, or you might bonk into one of the bats on the ceiling. At this point it isn't as important to stay off the cart, you're beyond most of the spawn points for birds, so just a short hop will do. Dash jump off the cart to the right when you get to the big exit point, you'll land on the edge of the platform in front of the door. This is actually faster than staying on the cart longer and hitting the door during your jump, because you have the added speed from your dash over a longer area.
100%[]
Regardless of route, the heart grab remains the same. For the heart, just fire a boomerang as you jump, it should curve upward and grab the heart. Missing it is of no consequence, you come back through this section another 4 times, so you have plenty of chances without slowing yourself down much, so just move on if it misses.
Waterless route[]
On the first cart, charge up c.sting. After the cart kills the flamingo near the pits, dash jump off the cart to the right, and release your charge right before hitting the bats on the ceiling. After the first drop, wait for the tunnel borer to break open the wall and go get the subtank. You should have plenty of time left of c.sting to get ahead of the enemy without getting hit by the instant-kill part of it. Try to avoid doing dashes along the ground, the dust will cause an absurd amount of lag, so instead just do a series of dash jumps until you get the tunnel borer off screen.
You can continue the stage as in any%, or use some more c.sting to avoid bonks before the second cart section, there isn't a significant difference.
Armadillo 100% bird despawning, visit, and fight
Despawning the birds in 100% is a little different toward the end compared to the any% version, to get your hadouken visit in. It starts the same way, after the narrow section with the bats and spike pits, do 4 full height jumps starting when the cart is halfway between the first two miners. X naturally drifts to the right during this process, so adjust yourself to the left a little bit at a time between jumps. Pause briefly after the fourth jump to avoid bonking the ceiling bats, then do another full height jump and start charging. Then do a short jump, then a medium-high jump. Ideally you land on the cart at or near the bottom of the final downward slope. If you jump too high or too late, you may land on the cart on the upward slope, which is very dangerous. If you land on the cart as it's jerking upward, you can clip through the cart and get knocked off (see http://www.twitch.tv/domalix/c/5074861) so it's important to do the right jumps to despawn the birds and land on the cart in the right places. When the cart launches off the ramp, dash jump off the cart, get your visit and go through the door.
Waterful route[]
You have a few choices of strategies here, either do (almost) exactly the same thing as in any%, except grab the heart, or do the bird visit. Something to note for waterful route, you don't have c.sting so you won't be getting the subtank on the first run through the stage, so be sure to remember to get it when you come back for the hadouken later.
Bird visit[]
Bird visit
The idea is to get hit throughout the stage in ways that do not slow you down, so you arrive at the end of the stage with 1-3 health remaining. Then, allow one bird to spawn, get the visit for hadouken, and land on the bird instead of falling into the pit, saving a small amount of time, like under 10 frames with all things considered.
Dash off the first cart immediately upon landing on it and have it push you forward. Hold left when you get hit to cut out your recoil and get off of invincibility frames sooner so you can get hit five total times from the first cart. When you leap off the cart, don't do a full height jump, or you risk grabbing one of the drops from the bats. The drop from the flamingo is not a big concern, it spawns really high so you can just dash underneath it. Don't kill either of the two bats before the first fall to avoid drops.
On the second mine cart, again you want to dash off, doing so very early isn't a big concern, just get hit once before the fall, then slide along the right wall a bit to avoid despawning the cart. You'll get hit by a bat here, then fall down, get to the right of the bats. Get hit by the cart, hop onto the cart, then jump off to the right to land to the right of the miners and on the upward slope. Repeat this process another two times, after jumping off the cart you should land to the right of the final miner in the hallway. Wait for the cart to reach you, then hop on and dash jump off.
The final section is the hardest, by this point you should have around 5hp if nothing went wrong. As long as you have 3 or more, you're good to go, if you have less than that you can grab the heart, which you'll need to get eventually anyway, for a free 2 hp back.
On the final cart, after passing the bats along the ceiling, jump off the cart past the miner, loop back and get hit by the cart as it goes down the slope. During your period of invincibility, dash jump off the cart to the right and get all the way through the narrow bat and miner section with the spike pits. Land in front of the next miner, jump onto the cart, and continue to despawn the bats like in the usual 100% method, with one exception. Stand on the cart during the final downward slope to get the right bird to spawn, then dash jump off the cart. You can release the dpad over the bird, and you'll fall right onto it after getting the visit.
Armadillo fight[]
any%[]
At the start of the fight, hop and fire a dash shot at armadillo. He'll always open with a roll toward you, a good pattern will make him come out of the roll when he crashes into the left wall, so you can set up a spark shot to hit him as he comes out of the rolling attack. Once his armor's off, the fight shouldn't be too tough. Just sit in the center and shoot him as he gets off invincibility frames, he only has one attack other than rolling (without his armor) and it's very slow. If he starts rolling again, just be careful and try to hit him when you get the chance, he's only invincible while rolling if his armor is on.
100%[]
Open with a charged spark. Then, like in any%, try to time a spark shot so it will hit armadillo if he comes out of his roll right after hitting the left wall and hold a charge again. If he gets hit, great, keep charging. If he continues rolling, just keep charging. If he comes out of his roll and you've got at least a yellow charge, just keep charging, since it'll be less than a second before your full charge finishes which does 6 damage. When his armor is coming off, charge up. Beyond that, just use uncharged spark shots to finish him off. There's a cf-0 strat involving spaced out sparks off the walls, but it saves a small amount of time, is easy to mess up, and relies in armadillo being in the right position. With practice, you can probably save a small amount of time with it, but there are probably better things to be practicing that save more time.
Hadouken revisits[]
“If you're touching ground it's a bitch visit” - colonelfatso
Get through the stage just like usual, grab the subtank if you're doing waterful route. For the hadouken visits you need, despawn all the birds like in the waterless route, then jump toward the ledge you need to see. Rather than continuing on and going through the door, though, turn left and drop down into the pit. If you catch the ledge, just dash off.
On visit number 5, you need to have every other item in the game and 32 health, then the hadouken capsule will appear.