+2 252+ SpA Fairy Aura Xerneas Dazzling Gleam vs. 252 HP / 0 SpD Aura Break Zygarde: 176-210 (81.8 - 97.6%) -- guaranteed 2HKO
0- Atk Life Orb Dark Aura Yveltal Foul Play vs. 252 HP / 0 Def Aura Break Zygarde: 64-75 (29.7 - 34.8%) -- 11.6% chance to 3HKO
252 SpA Life Orb Dark Aura Yveltal Dark Pulse vs. 252 HP / 0 SpD Aura Break Zygarde: 71-86 (33 - 40%) -- 99.8% chance to 3HKO
252+ Atk Choice Band Zygarde Stone Edge vs. 4 HP / 0 Def Yveltal: 164-194 (81.1 - 96%) -- guaranteed 2HKO
:(((
#SaveZygarde
It will either be amazing, or absolute shit. I'm willing to take that gamble for the whole crew.
Anyway, actual discussion here:
1) AV Landog was very much a thing late VGC15; might be decent against Lord Groudon while at least dampening Rayquaza's obligitory Dragon Ascent. Groudon as a partner completely dismisses Water as a weakness on it, and Delta Stream reduces Ice weakness + gains a Rock resist, while Primordial Sea says "nope, fuck off Sableye". Still viable?
2) Gyarados walls Groudon quite well; Rock Slide doesn't hurt that badly:
-1 252+ Atk Primal Groudon Rock Slide vs. 4 HP / 0 Def Gyarados: 72-86 (42.1 - 50.2%) -- 0.4% chance to 2HKO
252+ SpA Primal Groudon Overheat vs. 4 HP / 4 SpD Gyarados in Harsh Sun: 101-119 (59 - 69.5%) -- guaranteed 2HKO
252+ SpA Primal Groudon Eruption (150 BP) vs. 4 HP / 4 SpD Gyarados in Harsh Sun: 87-103 (50.8 - 60.2%) -- guaranteed 2HKO
And that's all assuming no bulk investment at all and you don't have Rayquaza negating the weather. Granted, Waterfall has surprising difficulty returning the KO:
252+ Atk Gyarados Waterfall vs. 252 HP / 0 Def Primal Groudon: 196-232 (94.6 - 112%) -- 68.8% chance to OHKO
With Primordial Sea / Delta Stream, it gains numerous, interesting benefits. Primordial Sea, again, blocks WoW, and Gyarados in rain is pretty painful in it's own right. Air Lock makes it pretty brutal on Pdon, Thunder Wave can snipe opposing Rayquaza too. Delta Stream reduces Electric weakness, makes Rock neutral, Ice is now resisted, and Gyarados' other resistances are still stacked on that, so it's basically only weak to Electric and has great resists. Pdon has probably crushed the hopes and dreams of the only popular Electric mons in VGC15 by now (Zapdos, Thundy, Rotom-W/H, Raichu) so that may actually be interesting for Gyarados.
3) Skill Swap Gengar + Pdon. lol.