>>41032569If it were to suddenly appear in USUM, I'd say that "what happens" is that Gyarados now has more variability in what items it is able to use. It can choose to nuke different things with Z moves, or it can use Life Orb for more consistent damage output etc.
For instance, a set of DD/EQ/Waterfall/Skydive would now be able to consistently beat Grass type checks like Tangrowth, deal solid damage to bulky waters, beat Mega Heracross and Keldeo, and it could now use Z-Waterfall as a nuke to take on Zapdos, Skarmory etc. which had previously walled the Z-Bounce set. All of a sudden, a lot of its checks disappear, and a lot of its counters merely become checks.
Zapdos was a 100% solid counter Gyarados' normal sets. With a solid Flying STAB and the ability to run Waterium-Z, Gyarados can now boost on the switch and OHKO with Z-Waterfall at +1 after Stealth Rock.
