Take this with a grain of salt because I haven’t experimented with this one, though I’m curious to hear from others. I do think Gyarados is on the cusp of having a niche. Being a flying type neutral to ice, optionally with intimidate, already renders it a decent switch-in to 4 of the best mons in the tier in Tusk, Zama, Lu, and Dnite, while outspeeding the latter two; adamant Gyara at +1 still outspeeds the standard IDBP Zama spread, though by a tiny margin that any speed creep will render moot. While it doesn’t want to switch into Kingambit, Woger, Hamurott, Weavile, etc., intimidate sets are useful in assisting with reining these threats in for others or itself. Its movepool includes many useful utility moves like twave, taunt, roar/dtail, and endeavor; lefties sub/twave/waterfall/phazing move is a (cheesy) set we’ve seen on paraspam teams already. Dragon dance sets with waterfall, eq, and double-edge/tblast flying/tera dragon outrage/scale shot have coverage for everything while either easing setup with intimidate or attempting to snowball with moxie. It handles most priority well, resisting bullet punch, aqua jet, and vacuum wave, while being neutral to ice shard, grassy glide, sucker punch, and shadow sneak and only weak to thunderclap. Raging Bolt is unfortunately a nightmare for it if you’re not tera ground/electric or substitute + eq, as can be Pult if you’re not Jolly tblast flying or outrage, Woger if you’re not tblast flying, tera dragon outrage, or tera normal double-edge, Zapdos if you’re not tera electric, and Dozo, Corv, Pech, and Kyurem in general. Certainly that is enough of a threatlist to satisfactorily explain why it’s not commonly used in OU, with the majority of teams being sufficiently prepared for it naturally at least unless it either takes on a more supportive role or is given significant support for its weak matchups. However, it seems strong enough to me to warrant occasional use on legitimate teams.