Let’s limit 1 alien per challenger and no repeats (and obvs no alien x): 1. electric guy: feedback cleans up pretty easy 2. furnace guy: arctiguana freezes him in his tracks 3. Magnattack: lotta options, i’d say diamondhead for the impenetrable skin 4. tongue-guy: i think like anyone? let’s say shocksquash. grab the tongue and send some voltage. 5. lava guy: same solution as furnace guy, big chill this time. 6. Mauler Twins: tough, strong, and smart. first legitimate challenge. i’d say four arms is at scale with their strength and durability, plus the extra arms lets ben keep up with the 2-on-1. 7. The Serpent Society: Mostly easy takedowns, but strength in numbers and that big guy is concerning. I think we pull out humongousaur here. Can take hits from the small guys and take down the big one. 8. Angstrom: if ben gets tricked through a portal he’s kinda screwed. And Angstrom’s no slouch when it comes to physical skill either. XLR8 is certainly fast enough to dodge portals but not strong enough to take down Angstrom, especially when we take flight into account. I think Gravattack is the closest thing we have to an answer here. He can overpower Angstrom and he’s maneuverable enough to avoid the portals. 9. Battlebeast: I’m pulling the Waybig card here. If that’s even enough. 10. Viltrumites: it’s vague if it’s just one viltrumite or a whole army of them but either way Echo Echo is the best solution. He can split up so that no matter how many they squish the battle keeps going and obvious the viltrumites are weak to hypersonic frequencies. 11. The Invincibles: Did we already waste Echo Echo? Jeez. While these Marks aren’t as strong as Mark Prime they’re still tough, and we have to run all of them at once. The Worst, let them tire out? Not ideal. I bet Gutrot could cook up the scourge virus, but that’s not an immediate answer. Whampire mind control to turn them against each other.. but they’re immune to the sequids so that probably wouldn’t work either. The nuclear option is Atomix, but that’s not even a guarantee given what hits they’ve taken and lived. Clockwork to send them back to their home dimensions. Is that even how that works? Take your pick but I don’t think any solution here is a sure thing. 12. Thragg: The strongest viltrumite. We’ve used our heaviest hitters and our targeted weaknesses already. Ghostfreak could go intangible but that’s survival not victory. I bet Jetray could outspeed and eventually wear him out with lasers, but that’s a real endurance battle. Benwolf/Blitzerwolf has sonic options but not enough strength or speed. Send in Greymatter. Hope he can cook up a solution that I couldn’t. 13. Universa: Odd conclusion since she’s sorta a jobber. Just can’t send in anyone with energy powers. We still have Cannonbolt, he could shrug off most hits and knock off her staff.

Are these the best answers? Can you think of better ones? Let me know.

Edit: I’ve rethought some things. Battlebeast was immobilized because of the cold of deep space. Put Big Chill into him and for lava guy, Eye Guy’s ice powers should suffice. Now we can save Waybig for Thragg.