The Many Asses of Dr. Mephesto is a story mission in the video game, "South Park: The Fractured But Whole".
Plot details follow.
Confront Mephesto about the mutant cats.
To start, head to Mephesto's Laboratory. After a short cutscene, it appears that you cannot enter the lab. However, wait awhile and Morgan Freeman will appear. He will bestow a new fart upon you. Use this power on the nearby fan to change from day to night. As you make your way to the lab, loot the three bags on the left and right of the path. Once inside, follow Dr. Mephesto to see the tour.
After the cutscene, you are faced with several many-assed cats. These foes deal a lot of damage, but more importantly, they deal massive amounts of bleed damage. Also, pay attention to the pee-filled containers. They deal a grossed out affect in a cross pattern when hit. Take out the first wave of cats to face even more feline foes. Focus on taking out the larger cats first. They have the potential to protect and increase the attack of their friends.
Finish the second group off to reveal one final wave. If you were saving your ultimate, now is the time to use it. Take out all the Many-assed cats to receive the Claw Scars costume.
After the next cutscene, head through the emergency exit to the right. First, loot the crate in here. Then, use Inspection Mode to interact with the green sludge on the ground. Use the Sandblaster to remove this toxic waste.
Then, use Haywire to fry the circuits up above. Now, use the TimeFart Pause to reach the battery. Pull it out before the timer expires. Next, use Diabetic Rage to move the gas tank from the path. Pull the battery to the other side. Use TimeFart Rewind to move the gas tank back out of the way. Place the battery in its socket to continue. Before moving on, go ahead and climb the ladder on the tank to reach the duffel bag containing a Cheesing Vial. Head through the doorway to meet the Mutant 6th Graders.
In this area filled with Mutant 6th graders, a battle is inevitable. You can lure them away by using Butters's Combat Buddy ability to hack the wires above the room near you. TimeFart Pause and hit the switch to distract the 6th graders with boobs. Do another Time Pause and hit the switch in the room to the left to show another screen with boobs. Now punch the Gorilla 6th grader to the far left to trigger the fight.
This is a very tough fight, but if you followed the above steps, a few of the enemies will be destroyed which will cause damage to the Giant Mutant 6th graders. The 5 Assed Apes boast very large health pools and hard-hitting attacks. While the Many-assed Sixth Grader Pigs deal massive damage upon death. As much as possible, kill them when they are next to their friends, not close to you. Large AOE attacks will come in very useful here.
With so many heavy enemies, you’ll need to dish out a large amount of damage fast. Also, be sure to use the electricity spires on the outside edge. Use knockback abilities to trigger shocks on the enemies. Finish off these 6th graders to receive the SphincterPlex artifact and the Gorilla Toughness DNA.
Before continuing through the door, be sure to loot the biowaste can behind the glass to find the Plasma Analizer artifact. Then, in the next room, you’ll face Mitch Conner. Take a selfie to record your evidence. Then head through the door on the left. First up, use the Sandblaster to remove the green goop. Then, before using your next buddy powers, loot the crate to find the Nuclear costume. Then, use Snap N Pops to expose the wires above. Use Haywire to hack in. Then, use Fartkour to reach the other side. Walk down the ramp to the left and loot the crate before Fartkouring again. Loot the box here before using Diabetic Rage to uproot the sealed door. Take this ladder down.
In this next room, you’ll face more Ass Mutants.
This fight is with less powerful foes than the last, but with a twist. The grates on the floor will telegraph before Ass Mutants from below spring up and deal 100 damage to anyone on the striped grates. Be sure to move all your characters away from the red tiles before the timer runs out.
Most often the mutants will end up on a red tile, be sure to let the timer run out if all of your characters are safe. Finish off these mutants to receive the Cloven Heirloom artifact and the Raging Hormones DNA.
Continue to the next room to face a gruesome choice. Here, you must either sacrifice your mother or father for the DNA scan required to access the elevator. Either option is unfortunate. Neither option is good. Make your choice. Then, place the required DNA in the scanner and take the elevator down.
In this hallway, loot the bag to find a Maximum Antidote and a Maximum Revive Serum. Before continuing, you have the option to add asses to the 6th grader leader in the test chamber. You pay $0.25 for each ass added to him, you can add a maximum of 5 asses, after that the machine will just spank him. Head through the next door to enter a cutscene and face Mutant Alternate Human Kite.
At the beginning, it seems like this fight will be impossible. The boss’s large health pool and the strength of your attacks are very mismatched in comparison. It hardly feels like you’re making a dent. However, eventually, you can use TimeFart Shift to change the time to day. Now your attacks will do much more damage. However, this period operates on a timer indicated on the bottom of the screen. Be sure and make your turns very quick to deal as much damage as possible before the timer runs out.
This fight is still very tough. You will want to spread out your team as much as possible. The boss can attack a whole column at a time. You will need to spread out in length and in depth. Also, try to get on the other side of the boss to isolate his AOE attacks. If you’re having troubles, be sure to come in with plenty of Revives and heals. It can be a long battle. Always prioritize keeping The New Kid alive. You need TimeFart Shift to keep weakening Kyle.
Once you finally drain Kyle's health pool, execute the button prompts to finish him off for good. You'll receive the Sentient Cyst as a reward.
Now go find Mitch Conner! Your final and biggest mission awaits, Farts of Future Past.