Hi,-snip-
I've run Veil+MGyarados myself on cart for a while, so i'll try to help you out on your team.
First of all just a heads up, EVs work a bit differently at Lv50 than they do at Lv100, so you want your EVs not being divisible by 8 to not waste EVs - especially since Hyper Training makes working with even IVs basically extinct (first stat number jump is at 4EVs, next at 12, then 20EVs and so on). It's nothing major by any means; you did put 248HP/8SpD on your Marowak set, so just as something to keep in mind for the future :)
I think your team might struggle with stall builds since you lack Taunt or similar tools to deal with it, so I would suggest using either Substitute or Taunt on your Gyarados, which helps against basically any stall team; Substitute will give you an even easier time to setup without fearing burns, para or toxic, but i think Taunt would be preferred to shut down any status moves including recovery on pokemon like Porygon2 too. You do have Mimikyu and Ninetales on your team so I personally think Ice fang on Gyarados isn't as needed, but with Garchomp on the team you could also go without Earthquake i guess, though there are many relevant targets for Ground coverage like Aegislash, opposing Magnezone and especially Tapu Koko once you've set up. Yes you miss out on hitting Salamence and Dragonite, but with (an admittedly frail) Ninetales-A, scarf Garchomp and Mimikyu on the team I think that's bearable.
On that note, Fairium Z > Ghostium Z is an option on Mimikyu, it lets you deal big damage against foes like Porygon2, Mega Kangaskhan, Mega Gyarados, Dragonite etc.; You will do less against Steel and Fire types with your Z move, but with Garchomp and Gyarados as teammates imo it's definitely something to consider.
Furthermore, as soLerme suggested, Celesteela would also help vs. stall with a standard Substitute/Leech seed set, with Aurora Veil on the team the Bamboo Ultra Beast can be even more annoying for opponents to face.
Marowak would still be a fine choice there, but post-bank there were many great Fire Types re-introduced to battlespot, which gives it tough competition as a bulky slow Fire type. If you don't want to run double-Mega (which could restrict in some matchups, eg.: if you need to beat Scizor/Ferrothorn and something like Mimikyu in the same match and would rather have a fire type along with m-Gyarados), I would suggest something like a bulky Rotom-Heat (@ Leftovers / Sitrus Berry) which has numerous options in Substitute, Will-O-Wisp, Toxic and Pain Split to help in tough matchups, along with great STABs (you could also run Firium Z to not lower your SpA if you need the Fire attack; Sash or Life Orb on Mimikyu is definitely a good option then, if you feel like 2 z moves are too restrictive for team preview), as well as a slow Volt Switch to bring in your other Pokemon without taking damage in favourable situations. This gives you a good answer to Steel pokemon like Kartana, Magnezone and Aegislash, which your team would have some problems with, and a good defensive pivot in and outside of Aurora Veil.
soLerme's suggestion of a Mega Charizard X does pair great with Aurora Veil though, if you are willing to take the disadvantages of having two Mega's; the combination of both Charizard and Gyarados on one team, especially with the Aurora Veil option, is extremely dangerous and hard to prepare for, since the potential Charizard Y makes things even harder for the opponent.
- Speaking of which, Charizard Y itself could be a great Fire Pokemon on your team too, with Drought keeping it from taking chip damage in the remaining Hail turns from Ninetales, while beating a lot of the current meta including bulky Water types (Tapu Fini says hi) your team could have issues with. A set of Flamethrower / Solar Beam / Hidden Power Ice / Flame Charge could work wonders with the possibility of Aurora Veil (standard Timid 252/252 spread, Flame charge is only there to let you set up and beat faster opponents it would usually faint to).
I know these were quite a few options, feel free to try a few and decide which suit your taste the best, or ignore some of them if you'd like to :D