The enemies in the 1 vs 100 challenge are all black Helix clones. They're likely all failed prototypes or copies of him like the one we've seen in Helix's stage. It can become Fridge Horror depending on the level of awareness the clones possess...
Kid Cobras swirly spine is a bit unnerving, but it is shown that the arms phenomenon is capable of affecting other parts of your body besides your arms like your eyes and hair, so he could also be affected by it in his spine, just not enough to get it spiral all the way at least once.
This may also explain his heterochromia iridum. Having the ARMS ability gives one Exotic Eye Designs, and Kid Cobra has two kinds. One set of ARMS could be his snake arms, and the other could be his spine.
Why are Max Brass's ARMS the championship belt when he probably started off as a contestant himself? ARMS seem to change depending on what the user associates with, and of course he would have been associated as the World Champion!
It's also possible Brass was a champion before getting ARMS power, that all his different belts are from the competitive divisions of another combat sport, from multiple combat sports or multiple competitive divisions of multiple combat sports.
All of Mechanica's default ARMS perfectly match her mechanic hobby. The electric Revolver matches her working with electronics, the hammer-shaped Whammer matches her building and using tools, and the exploding Homie matches her using scrap metal for her projects (assuming the Homie produces any scrap metal).
Why does Twintelle have the ability to slow time, and why are one of her default ARMS the Chillas? Because she's a literal show-stopper.
Each of Lola Pop's Palette Swaps match different kinds of sweets. Her default is more in line with fruit-flavored candy, such as orange and strawberry. Her blue and pink is similar to sugar-based sweets like cotton candy and bubblegum. Her green and orange brings to mind caramel apples. And her brown one seems to be based on chocolates.
While Mechanica is her most obvious foil, Dr. Coyle seems to have the most animosity towards Max Brass, Twintelle and Misango.
Misango in particular makes the most sense thematically. Dr. Coyle has been rigorously studying biological, mechanical and electrical engineering for decades in her efforts to become the strongest ARMS fighter. Misango not only has a leg up on her simply by getting ARMS power by random chance, but he's more versatile in battle than she is simply because the society he was born in has been doing similar things as Coyle for a much longer time. Then consider he's in the Grand Prix to tell everyone that his ways are best. Mechanica is amusing but inferior, Misango has everything Coyle wants and, from Coyle's perspective, is taunting her.
Once you get past her obsessive activities and self centered arrogance, Dr. Coyle is only slightly worse than a standard football hooligan. Max Brass is the only person she tries to cause serious injury/potential death too, and that was after years of pent up personal animosity. Years of personal animosity might also mean she may know him well enough to expect him to walk off a blow that knocks him off a building and through another. Crashing his sporting event out of spite may have been Coyle's only motivation there. With that in mind, Coyle's interest in Twintelle may be the belief that Twintelle is the only "test subject" she can indefinitely extract material from without causing much pain. The fact none of the test subjects are voluntary would have regulators shutting her down, but Coyle may abide by some ethics all the same.
Min Min being able to turn one of her ramen arms into a dragon may seem fairly strange, since Chinese Longs are associated with life, storms and pearls while ramen isn't. But it makes sense considering those things are related to water, which ramen is cooked in.
There is no way to predict when the ARMS phenomenon happens or who gets it. Someone could just wake up one day, and their arms are gone and replaced. While it's stated that the general populace knows about this, it's very jarring and unsettling to consider the idea that your body could be radically changed overnight with no way to prevent or fix it.
That said, there seems to be no downsides to this, and they seem perfectly capable of functioning normally outside of fights.
There also doesn't seem to be an indication that you get to choose what your ARMS are made of. Sure, having springs for ARMS might be "pretty rad," but how about other materials? Not to mention for some people, those ARMS become their defining character trait.
The ARMS one receives seem to be based on already defined traits that you're probably okay identifying with. Spring Man trained at spring gym, Minmin was the mascot for a ramen shop, etc.
Not knowing who it awakens in and when should be elaborated on. When competitive fitness nuts like Spring Man or Max Brass get it, when hard working entrepreneurs like Ribbon Girl and Twintelle get it, when glory seeking performers like Kid Cobra and Lolapop get it, when prodigious students like Ninjara and Min Min get it, that's all well and good, assuming ninja serve the public in this setting. But the possibilities of what more unscrupulous individuals can do with ARMS power they can in no way be barred from attaining and may not immediately be recognized as having, are endless. Endlessly horrible before you consider ARMS power seems to be capable of "awakening" the dead so long as their bodies are decently preserved. Again, it's fine a loving family man like Master Mummy was brought back to life, but an ARMS related tragedy could happen at pretty much anytime.
It's stated that Dr. Coyle experimented on Master Mummy, ultimately leading to his reanimation and new powers. Sounds like it wouldn't be random chance that the dead would come back with ARMS. Still creepy to think about, though.
How does Hedlok control his host? From what we've seen in the trailer, it isn't voluntary, and it may very well be painful. We also have no idea if the fighter he controls is aware of what's happening, or they have no memory of it. Or could it be something even worse?
Helix is not fully self-aware yet, confirmed by one of Biff's comments about him. The other fighters are beating up someone who doesn't realize what they're doing, and Helix always seems remorseful whenever he wins a round, indicating he might not like what he's doing.
Although Helix seems happy in his ending image. Maybe he's learned the sport is all for fun!
While Helix may not be fully self-aware, he definitely knows what the sport is and how to play it. He did leave his lab and birthplace specifically to join the Grand Prix, after all, and likely went through some kind of registration process. When he wins a fight, considering how he stretches himself upwards when he wins, he may be trying to get a better look at his opponent, possibly to check whether the opponent was defeated and/or to check if the foe is okay.
