Steelnea: A fantastic bulky attacker with the power to run AV sets or offensive utility sets. Metal Burst is going to be one of its best moves, as its high HP, immunity to Toxic, and low speed means it will likely be able to hit something hard with it. Diamond Storm on the AV set can increase its Defense and deals with Fire types that might like to trap it. I don’t think it’s broken though, especially with most things packing Ground or Fire coverage anyway.
Terreon: Nasty Plot was the breaking point for me, looking at this thing. Sure it’s not taking too much physical damage, but with its high speed and a Nasty Plot boost, will you get that damage off in time?
Flamepion: A Trick Room setter with Spirit Shackle, reliable Psychic, Steel, and Fighting coverage, Wish, Final Gambit, and you can’t Knock Off it’s item thanks to Sticky Hold? I think that’s pretty good.
Vultena: We already have an Electric Surge setter, and we already have Electric powerhouses. Stats are very minmaxed, so it’s redundant and broken.
Antestar: The most bizarre, counterintuitive abilities you could see. Toxic Boost on a Steel type, Innards Out on a mon with 18 base HP, and Wimp Out in general. It has solid potential as a mixed mon, with Fairy and Steel STAB, U-Turn, Earth Power, Seed Flare, Bonemerang, Psyshock, and even Sticky Web for some reason. Very much a glass cannon, but not explicitly broken.