Spark Mandrill's stage is a power plant. If you come here after beating Storm Eagle's stage, Storm Eagle's air ship has crashed into it, causing some changes, the most notable change being blackouts in places there were no blackouts before. This makes the level a bit tougher, but it also makes the miniboss here significantly easier, so if you're having trouble with him, feel free to fight Storm Eagle first. He's not that tough even if you don't have the weapon he's weak to.
Anyway, proceed to the right, climbing up and down the ladders as necessary. You'll fight some Gun Volts while avoiding the currents in the floor. Certain spots will generate sparks that move along the floor and will damage you if you touch them. These don't appear if you've beaten Storm Eagle.
Sub Tank
If you have the Boomerang Cutter, you can pick up a sub tank in this area. When you reach a point with two ladders, take the low one and continue right until you see a Sub Tank behind a wall, then fire a Boomerang Cutter at it to retrieve it. If you collect health while your health meter is full, it will be stored in the Sub Tank for use later. Handy! Don't bother to climb the ladder here. There's nothing there. Afterwards, head back to the spot where the path branches.
The next area gets dark as soon as you enter, but not so dark that you can't see the ground unless you've beaten Storm Eagle, in which case you'll need to be extra careful. You'll also encounter a new enemy.
Hotarion
These things quickly fly from one side of the screen to the other and will damage you if you touch them. They leave a trail of light behind them making it easier to see where you're going, but it's really not necessary since you have enough light to see the platforms anyway and the enemies aren't affected by the lighting. You should continuously be shooting in front of you to be taking these things out as they appear.
Deal with the Hotarions and Flammingles and continue onward. When the light returns, head down the ladder and get ready for a miniboss.
Thunder Slimer
He moves around the screen in a giant blob of goo, throwing balls of slime that will stick X to the floor. He also has an electrical attack that he'll fire straight down, so avoid that. You'll know it's coming when he moves to the middle of the ceiling and charges. The range of the attack is smaller if you've already beaten Storm Eagle. Make use of the walls and remember that you can dash jump from them by pressing the dash and jump buttons at the same timing, making it easier to get away from the boss when he gets too close. He has 46 HP so he'll take a while to go down. Make use of your charged shots. Storm Eagle's Storm Tornado and Flame Mammoth's Fire Wave are both pretty handy against this boss.
After his flashy death scene, keep heading right until you meet a new friend.
Rush Roader
This guy basically just runs back and forth until you put him out of his misery. They take six shots to take down, and they'll start freaking out and staying in place after you do enough damage, making them easy to finish off. They're not difficult, but they're quick.
You'll also meet a certain turret enemy for the first time.
Turn Cannon
These are stationary and follow the predictable pattern. They fire two shots at a time, alternating firing to their sides and 45 degrees up from their sides. (They can be attached to walls and ceilings so it's relative to whatever is "down" to them.) Once you figure this out, they're very easy to avoid, and can be taken out with a few shots of your own.
Continue right and up the steps to meet a giant turtle.
Mega Tortoise
These guys have a decent amount of HP (16) and take up a lot of horizontal space on the screen. They fire mortars that will land exactly where X is standing at the time, but they're slow and easy to dodge, except for the fact that these guys often appear in areas with little room to move left and right. Mash that attack button to take them out quickly.
Heart Tank
Right after the Mega Tortoise and before heading down the ladders, look up. There's a Heart Tank on a small ledge near the ceiling. There are two ways to reach it. First, dash jump off the wall and quickly move back towards the platform, then wall jump up. It's pretty tricky, but there's no penalty for failing so try as many times as you need to. You'll need the leg upgrade for this one. Alternatively, fire a Boomerang Cutter at it.
Now head down the ladders, being careful not to get hit by the enemies. (Charge your shots before dropping off the ladders.) Head right and take out some more Mega Tortoises and head up. Next you'll reach another dark area with some Hotarions and Balls De Voux. Remember that if you start backtracking, there's a chance a Hotarion will spawn on the left side of the screen instead of the right. This parts a bit harder than the earlier dark area, but basically similar and the same basic strategy of firing in front of you applies. Next up is the boss!
Spark Mandrill
He's big and electric and he hits like a ton of bricks. We can beat him, though.
The Hard Way
Be careful of the walls! He has an attack where he dashes across the screen and punches the walls, causing you to detach them from them and land right on Spark Mandrill and take a chunk of damage. He can also cling to the ceiling and drop on top of you from above. If he's standing on the ground, he can punch the ground and cause balls of sparks to come out in either direction, which will crawl along the floor, up the walls, and even along the ceiling. The real kicker is that punch, so don't rely on the walls too much. If you're quick, you can dash jump over him when he starts his dash punch. Spark Mandrill is pretty tough if you're not prepared.
The Easy Way
Fortunately, we are prepared. We have his weakness, and this fight will be over in a few seconds. Shoot him with the Shotgun Ice and he'll freeze in place for a moment. When he breaks out of the ice, immediately shoot him again and he'll freeze again. Time it right and he won't even get to move! A steady stream of Shotgun Ice blasts and he'll be helpless before you. If he does get away from you and jump up to the ceiling, fire at whatever wall is farthest from him and it'll reflect back at an upward angle and hit him, dropping him to the ground.
Of course, you'll get your prize for beating him either way.
Electric Spark
Fire a slow-moving ball of electricity forward, when it hits a wall, it will split in two and move along the wall in both directions. The energy balls will continue along the same path through the air even if the wall ends. Charge it with the arm upgrade to send a wall of electricity out to either side.
What's Next?
Nothing special, really. This new weapon isn't bad for dealing with enemies in certain situations, but it doesn't do anything special, and clearing Spark Mandrill's stage has no effect on any other stage, so let's just move on.
NEXT: Armored Armadillo
