Waybig is canonically the 2nd strongest alien Ben has unlocked. Obviously Ultimate Humongosaur and Atomix could give him a run for his money, but master control with XLR8 is basically optimal defence.
Ultimate Waybig obviously slaps pretty hard, and therefore is another contender for the strongest single alien in the mix.
So, here's my reasoning for how OS Ben wins...
First, make a little pod of Taydenite. He'd honestly be the kind to wait and see what kind of awesome aliens future him has. In the pod, he goes Greymatter and has a little think, watching and waiting, trying to stay back. I'd assume most future Bens would know not to really bother spending ages bashing through Taydenite, and since OS Ben isn't doing anything, he's obviously not the main target. I'd guess they'd swarm UA Ben, since he has the single strongest alien among them, with Ultimate Waybig.
Then, use Ghostfreak to sneak through the floor after gathering how all-out the others are going. Get to whoever is the most isolated, swap to diamondhead, trap them in Taydenite. I'm gonna assume this would be what seems to be the weakest one here, in the form of Reboot Ben. He just hasn't got anything real special, simply being an inferior OS/AF mix. Maybe Rath could get some good hits in, but OV or AF could feasibly delete a single Young Appoplexian, be it with a Young Adult Incursion Warrior (Bullfrag, sorry if I got the species wrong lol) or just freezing/trapping him with Diamondhead or Big Chill. Plus, he starts as Cannonbolt, who has some horrid matchups here- Goop, Big Chill, Gravattack just turning him into a small, spinning planetiod...
So, we have one down, being Reboot. If needs be, you could use BenVicktor to shock him a bunch, putting him properly out of commission. Wasn't expecting anything from him, honestly. There's a good chance OS is noticed here, so now the real fighting begins. We'll say he tags to Benvicktor, since he's generally a pretty solid alien.
First is the hardest matchup, by a long shot. OV Ben. Feedback is a nightmare to deal with, absorbing all of Ben's energy attacks, and using electricity, something only BenVicktor really counters. So, there's one last trick here that could work... the OS watch's failsafes. Yes, the green energy blast thing. It's not an on-command attack, so here's a way to bait it out, but I'm sure you could do it with a few others. Bait OV into using Feedback's absorption, via a lightning blast from Benvicktor. Let OV get comfy with this fight, knowing Vicktor is kinda weak here, until he tries to go for a closer-range absorption. Then, simply leap at the hands, wrists first, and detransform, hopefully getting Feedback to unwittingly absorb the watch's energy. This seems to consistently force out the energy blast, hopefully taking feeback down. If not, XLR8 could deliver some quick blows while OV is still recovering.
Then, there's AF. (I'm saving UA for last, since Ultimate Waybig is terrifying.) There isn't really one winning strategy here, honestly. They've both got pretty solid counters to each other, and both have Master Control, so I think OS' best bet would be trying to use XLR8 to find an opening, then quickly tagging to Fourarms for a strong hit. Humongosaur is pretty scary here, but not super fast, so Wildvine could try trip him up, or block his view with Seed Pod Bombs. This is the only one I can't really give a winning idea for, so I suppose it's a matter of opinion. I do, however, believe AF loses to UA, so I'll move OS Ben on saying that either OS or UA would take down AF.
Finally, UA. Last 2 competitors. UA most likely uses Ultimate Waybig here, for obvious reasons, so here is where the fight gets a little dicey. UWaybig was able to survive attacks from the Dagon, something I doubt OS Ben could really scale up to. So, the only real choice is to force UA out of being Waybig. 2 Methods come to mind- placing UA in a situation where Waybig simply isn't practical, like an enclosed space, or when dealing with something small, fast, and hard to hit; or placing OS in a position where he is able to simply stall until UWayBig times out. So I say, why not do both?
First, go back to Frankenstrike. UWayBig is made of some type of metal, and since BenVicktor can create Electromagnets using metal, simply do so, as to stick onto Waybig's body. This makes it impractical to actually attack OS, since it would risk UA harming himself. Slowly move to about halfway up UWaybig, using the weird shapes of Waybig's torso, waist and legs as barriers. BenVicktor is pretty bulky, so a few hits would be feasible, if mostly ineffective. Then, use Wildvine and Benmummy to potentially bind some of UWaybig's movement, if only shortly. This is all just buying time. Diamondhead can create great shields, plus threaten actual damage to UWaybig with Taydenite shards. Keep going until UWayBig Ben times out or tags out. If he times out, then boom, victory. If he swaps, Master Control allows for counter-picks to any Andromeda, and Chamalien or Juryrigg won't be of much use. Fasttrack is considered slower than XLR8, so that's a no-win scenario there. Clockwork is a big threat, but with enough XLR8 boosted reaction time, using Upgrade to merge with him could be a great solution. Regardless, OS simply needs to keep countering and playing defensively until UA times out fully, before finishing the fight.
Of course, OS would likely just run up and try to deck someone with Fourarms, getting horribly blasted in the process, but hey. He's definitely got a good shot.
