Normalize Regigagas - Very interesting idea. It always makes me wonder what GF was doing when they made a pokemon like Regigagas that's supposed to be the trio leader and give it a horrific ability designed specifically to make it worthless in battle.
Normalize makes sense flavourwise and acts somewhat as a nerf in terms of severely limiting coverage (being useless against ghosts and generally ineffective against bulky steels) but at the same time opens up a whole lot of new playstyles that might revolve around using this ability. Probably my second favourite after my own submission(Mega-Steelix) but that could easily be the bias talking.
Tinted Lens Zygarde - I haven't really used Zygarde before, but tinted Lens definitely gives it an edge over other DD sweepers, that said I don't think it brings anything terribly unique in terms of playstyle to the meta, you'd still be using it in the exact same way it would just get a bit more of a buff offensively that lets it compete with other DD Sweepers.
Adaptability Galvantula - Solid buff, definitely makes Sticky web likely to be more viable due to Galvantula itself becoming more viable. I like it, just not as much as the others, probably because Galvantula already has somewhat of a niche whereas both Regigagas and Steelix are in the depths of NU, and I'd rather see some new faces in OU.
Arena Trap Mega-Steelix
My own submission, frankly I was extremely disappointed with Mega-Steelix, which despite an awesome design got such a disappointing ability.
I figure Arena Trap fits flavourwise and not only gives it viability in OU, but also versatility.
So while M-Steelix's Arena Trap doesn't activate on the first turn, you could potentially run Roar, expecting your opponent to switch into his most threatening special attacker, only to phase it out and ensure that the pokemon that ends up being trapped is *not* that pokemon. Running a pink blob or Sylveon would also help reduce the risk of special attackers, and they can also pass on healing to Steelix who doesn't have reliable recovery of its own outside of rest.
M-Steelix could also boast a set-up set of Curse, Rest, Gyro ball and Earthquake/elemental fang if you're desperate for different coverage. It can switch in on a lot of common pokemon and set up with ease, especially pokemon locked into specs/scarf/band, like Volt Switch Magnezone or Bullet Punch Scizor. It also works well as a "reverse trapper" for pokemon like scarf Gothitelle or Wobbuffet.
It does well vs most stall teams due to being immune to toxic and paralysis. It also quad-resists stealth rock which is a nice bonus.
Steelix is also a really great way to put your enemy cleric (Chansey/Blissey, Sylveon, Clefable, etc) out of comission. The opponent might have to think twice before bringing in one of the aforementioned to heal bell or wish pass if they now it will guarantee the KO of that mon.
The biggest issues with M-Steelix are
1)That it doesn't get it's ability on it's first turn. This however I feel helps stop it from becoming too overbearing to deal with as a trapper, it also allows for mind games where if your opponent has an obvious switch in you can double switch into a counter of your own and get a free turn, or simply set up Stealth Rock or if so inclined run coverage moves that surprise your opponent (e.g. Stone Edge/Crunch/Aqua Tail/Ice Fang) and kill/weaken potential switch ins.
2) It's low speed and vulnerability to Special attacks. This makes it very easy for a number of pokemon to revenge kill it, which also, I feel, helps stop it from becoming too overbearing, as even if a player manages to get a Steelix Curse set up on a viable target, you'd still have had to eliminate most Sp. Attackers on the opponents team in order to guarantee a sweep.
3) And of course, one thing to keep in mind is that Arena Trap doesn't work on Flying/Levitate pokemon.
That said, I feel like M-Steelix would have just enough flaws to make it a manageable threat while still immensely improving in viability as well as having the flexibility to run various different sets depending on team needs.
Between Iron Defense/Toxic/Rest/Filler and work as a stall mon, or Curse/Rest/Earthquake/Gyro ball as a boosting set, or Stealth Rock/Roar/Earthquake/Heavy Slam as a SR setter/phazer, or Earthquake/Heavy Slam/Ice Fang/Stone Edge as an all-out attacker, or any combination of those, there are so many roles that M-Steelix could fill, each of which could fit on different styles of teams.