Armored Armadillo's stage takes place deep underground, and is full of a bunch of robots wanting to meet you. It features a fun sequence where you get to ride on a cart and on top of this, you'll also be able to grab a heart tank and a sub-tank (if you're fast enough, that is).
Begin by going to the right and jumping on the red mine cart. It will immediately accelerate and begin to go down the track. Don't even worry about shooting any enemies; just let the mine cart obliterate anything that steps in its path. Towards the end, however, is a gap, so jump off of the cart as it's about to fall in to make it to safety.
Keep going to the right until you come to a larger gap: slide down the left side and once you hit the ground, you'll be greeted by a friendly (but killer) dig machine. Immediately scale the wall again and stay there, having the dig machine pass you. Once it has, drop down and go into the area the dig machine was in; inside, you'll find a nice Sub-Tank. Take it and follow the path the dig machine took, encountering bats and helmet robots a long the way.
Eventually, you'll get to another red mine cart, so jump on this one and enjoy the ride (just let the cart do all of the work). Once you get to the end, you'll come upon another large gap. Make sure you have Flame Wave equipped and then jump down, where you'll land right behind another dig machine.
Start shooting it with Flame Wave until it's finally destroyed, then continue down the path, where you'll see a Heart Tank on a ledge. Jump up on the ledge and take it, dropping back down and continuing down the path. It is also possible to slide infront of it, allowing you to get to the Heart Tank without using the Flame Wave
You'll come upon the last red mine cart, so jump on it and sit back (yet again). At the end of the track, you'll see some robot birds: this means that the exit is near, so start shooting the birds and prepare yourself for a long jump. Once you get to the end of the track, the cart will fly off; immediately jump, which will cause you to land on a ledge (or a wall) on the other side of the area. Step into the dungeon and prepare to fight Armored Armadillo.
Maverick boss: Armored Armadillo
This guy should be a pushover with his weakness, the Electric Spark, but his annoying rolling attack may sometimes cause problems. He'll start the fight off by rolling into a ball and crashing around the room, which is one of his two basic attacks. In this form, he moves fast, but his pattern is easy to spot (he'll go across the room in a diagonal pattern) and his movements are easy to dodge. The trick with this boss is his shields. He's normally very guarded and will block attacks with the shields on his arms. Plus, with the armor on his back, he's invulnerable while he's in his rolling attack. You have to catch him off guard, such as when he's just coming out of the rolling attack. Thankfully, one hit from the Electric Spark in this state will make the armadillo drop all his defenses. From then on, he can be hit anytime, even during the rolling attack.
Now he's very vulnerable, and he'll resort to shooting some plasma bolts from his cannon. Simply scale one of the walls and hide in the corner until he's done, in which he'll then go into his ball form and attempt to crash into you. When he's heading toward you, just drop down and stay there, and dash out of the way when necessary. He'll then come out of this form, so shoot him again with his weakness. He'll then go back into his ball form and then come out of it again, repeating this until he's finally defeated.
Rolling Shield! This fires a large round orb at enemies, and on contact with one, will explode. If it hits a wall, it will simply bounce off the wall.