252 SpA Choice Specs Keldeo Hydro Pump vs. 252 HP / 0 SpD Tentacruel: 114-135 (31.3 - 37%) -- 85% chance to 3HKO after Stealth Rock and Black Sludge recovery
Not that Tentacruel is common anyways, and what can it do in return?
Well, I suppose our experiences with seeing Tentacruel differ as I see him get a fair amount of usage honestly. Accuracy is one of the big factors why I run Scald/Surf over Hydro pump. The added PP is also a nice bonus. There's not much a Tentacruel can do to you, but Hydro Spam on it leaves a window for him to Toxic you which isn't too bad, but damage is damage. Also that's 3 of hydro's 8 PP gone to Tentacruel.
Hidden Power [Flying] accomplishes the exact same thing while getting better coverage.
252 SpA Choice Specs Keldeo Hydro Pump vs. 4 HP / 0 SpD Mega Charizard Y in Sun: 236-278 (79.1 - 93.2%) -- guaranteed OHKO after Stealth Rock
It does more than HP [Electric].
Scald and Hydro Pump Vs a Mega Zard Y in the Sun are both an OHKO after Stealth Rocks. Without rocks they're both 2HKO's.
252 SpA Choice Specs Keldeo Scald vs. 4 HP / 0 SpD Mega Charizard Y in Sun: 170-204 (57 - 68.4%) -- guaranteed OHKO after Stealth Rock
Aside from hitting Bug types and Hitting for Quad. damage on Grass-Fighting types (Breloom, Chesnaught), I don't see what else H.P. Flying hits that H.P. Psychic doesn't hit already x.x Furthermore I don't really see much bugs to nail with H.P. Flying
252 SpA Choice Specs Keldeo Scald vs. 0 HP / 4 SpD Galvantula: 292-345 (103.9 - 122.7%) -- guaranteed OHKO
252 SpA Choice Specs Keldeo Hidden Power Flying vs. 0 HP / 4 SpD Galvantula: 147-173 (52.3 - 61.5%) -- guaranteed 2HKO
252 SpA Choice Specs Keldeo Hidden Power Flying vs. 252 HP / 0 SpD Scolipede: 264-312 (81.4 - 96.2%) -- guaranteed 2HKO (H.P. Psychic does the exact same damage).
252 SpA Choice Specs Keldeo Hidden Power Psychic vs. 4 HP / 0 SpD Breloom: 294-348 (112.2 - 132.8%) -- guaranteed OHKO
252 SpA Choice Specs Keldeo Hidden Power Flying vs. 4 HP / 0 SpD Breloom: 588-696 (224.4 - 265.6%) -- guaranteed OHKO
252 SpA Choice Specs Keldeo Hidden Power Flying vs. 252 HP / 0 SpD Chesnaught: 496-584 (130.5 - 153.6%) -- guaranteed OHKO
252 SpA Choice Specs Keldeo Hidden Power Psychic vs. 252 HP / 0 SpD Chesnaught: 248-292 (65.2 - 76.8%) -- guaranteed 2HKO after Leftovers recovery
H.P. Flying seems a bit Overkill in these situations while H.P. Psychic is just enough to nail them while providing solid Poison coverage.
252 SpA Choice Specs Keldeo Hidden Power Psychic vs. 252 HP / 0 SpD Chesnaught: 248-292 (65.2 - 76.8%) -- guaranteed 2HKO after Leftovers recovery
252 SpA Choice Specs Keldeo Hydro Pump vs. 252 HP / 4 SpD Azumarill: 160-189 (39.6 - 46.7%) -- 34% chance to 2HKO after Stealth Rock
252 SpA Choice Specs Keldeo Hydro Pump vs. 4 HP / 0 SpD Gyarados: 134-158 (40.3 - 47.5%) -- guaranteed 2HKO after Stealth Rock
252 SpA Choice Specs Keldeo Hydro Pump vs. 252 HP / 0 SpD Mandibuzz: 280-330 (66 - 77.8%) -- 25% chance to OHKO after Stealth Rock
Seriously, it only needs Hidden Power [Flying]. I use mine under rain and holy jesus:
252 SpA Choice Specs Keldeo Hydro Pump vs. 252 HP / 4 SpD Mega Venusaur in Rain: 171-202 (46.9 - 55.4%) -- guaranteed 2HKO after Stealth Rock
Nothing can safely switch in u.u
A rain boosted Hydro Pump is somewhat pushing the situation in your favor to allow the 2HKO on Mega-Saur. I don't have the leisure of rain support all the time. Missing Hydro on Mega-Venu and on Azumarill however may cause death by Giga Drain or Play Rough. Generally I'd rather have the Azumarill and Gyarados switch in on a Scald and hope for the burn (which 30% may be low, but It does trigger and It helps a lot) and switch Keldeo out to something to else.
Hydro Pump is something to fear by itself, yes. But that doesn't mean it has to overshadow the other moves Keldeo could use. Also I'm butthurt about missing it all the time, srsly lol.