Originally Posted by Fat voodoo pimp
Hydreigon outspeeds every unboosted Pokémon in Tailwind with no investment, so unless you want to target a Scarfer or be faster outside of Tailwind it doesn't really need any speed. Maybe enough to beat Kingdra?
As for your second question, not quite:
252SpAtk Fight Gem lvl 50 Hydreigon (+SAtk) Hidden Power (Fighting) in Sandstorm vs 252HP/0SpDef lvl 50 Tyranitar (Neutral): 83% - 98% (172 - 204 HP). Guaranteed 2HKO.
Originally Posted by Fat honchkro13
Modest max Sp. Attack Hydreigon with a Fighting Gem boosted HP Fighting deals 83.09%-98.55% to an Adamant 252 HP/4 Sp. Defense Tyranitar without Chople Berry.
Without a Fighting Gem, deals 56.04%-67.63% to the same Tyranitar.
You're basically looking at a 2HKO with or without the Fighting Gem, so I'd change the item if I were you.
Ah ok, I thought it would be a 2HKO, but I wanted to double-check since I didn't have access to damage calcs at that time. Since I don't really feel like gambling with Focus Miss, I'll just find another way past Tyranitar then.
And so no Speed investment, gotcha. I'm experimenting with the possibility of B&W2 Unova Pokemon as part of VGC 13 later on, and Kingdra doesn't pose a problem as of now, so I guess I'll just invest in HP and SpA.