5th Gen How did you defeat Ghetsis' Hydreigon?

Generally speaking, Hydregion was sort of a fearful Pokémon back in generation five of games.

Nowadays, it's kind of overlooked, as it has more weaknesses than it did before (thanks to introduction of fairy, which this Pokémon is four-times weak against, if I'm not wrong), but during then, Hydregion took some time to counter, at least from my end; it's pretty fast, and also hard-hitting on both physical and special sides.

How did I manage to defeat? Sadly, I'm not too sure, as it's been a while since I had actually fought Ghetsis in BW. Though, if I were to try my best on remembering something, I would say I had used some bug-type attack (likely U-Turn); Scizor was one of my core team members, and it did have access to a couple of bug moves in its set.

lol, moonblast

But no, I used my Heracross. <3 Hydreigon can't take an X-Scissor.

^ Well, Heracross isn't in BW, unless you're talking B2W2 (which, again, this isn't about). But I remember one person I follow on Twitter, when she did a Nuzlocke on White last summer, she claimed that her Mienshao (which was like Level 52 or 53) managed to OHKO the Hydreigon with Brick Break, despite being slower. I don't remember if she had the Expert Belt or not, because you'd need THE strongest moves to OHKO it.

Nothing in the Unova Dex walls Ghetsis' Hydreigon in BW. If you're going to take a hit, you need to OHKO him back, which is extremely difficult. Scolipede can probably outspeed and OHKO with Megahorn, but that's just a guess. Conkeldurr with Hammer Arm could probably take a hit and do it, too. Mienshao can try a OHKO with Jump Kick but, if it doesn't outspeed, it'll need to take a hit, and it's quite frail.

^ Or Low Kick with Conkeldurr, which does 100 base damage to Hydreigon.

And for the sake of calculation...
Level 51 122 Attack Scolipede Megahorn vs Level 54 180 HP/118 Defense Hydreigon (which it has, unless it's a Hasty nature): 140-168. Not enough to OHKO, but it does a big chunk. Random numbers I came up with for the Attack and level, but it does get my point across a bit. It doesn't help that Hydreigon is +Speed natured (which I learned from the finale of Marriland's Black Wedlocke), so it's likely to be faster than anything you throw at it, unless you have, say, a Haxorus with Dragon Dance, as I mentioned in the OP. With the Expert Belt, however: 168-201, giving a high chance to OHKO it.

Now I know that Sawk with Close Combat can OHKO it (because i've done so before), which is helped if it has Sturdy. And the Conkeldurr that I mentioned before (Level 52, 188 Attack, no boosting item) had a guaranteed OHKO with Low Kick (100 base power on it), even without the Stealth Rocks I had set up beforehand (182-216, which is BARELY guaranteed).

I believe I had Archeops used Dragon Claw in order for her to defeat Ghetsis' Hydreigon. I remember grinding a bit until Archeops learned the move and also had her holding something that slightly increases Dragon type moves, so yeah haha.

Not hard My friend's Dialga massacred his whole team no problem

I beat it in 2 hits with Samurott's Ice Beam. His Eelektross was a bigger problem for me than Hydreigon.

I hit it hard and fast with my Conkeldurr. I don't remember the moveset my Conk had but it was the only thing I had on my team that could have beat it so it must be what I used. That was one battle where I did actually have to use status inducing moves to win so that was a first.

easy;my conkell durr was burned from cofrgrigus and it have guts and holding a quick claw
so i used a dynamicpunch on hydeageon with the quick claw and guts...1 HIT-KO

I kind of got lucky with Scrafty... I also made my pokemon's level higher than his.. so I didn't have much problems... Though he did kill my Scrafty, I remember using an Electric pokemon after, for I thought Hydreigon was a flying pokemon at that time.

I just used my own Hydreigon.It might have taken out some of my other pokes though.

I don't easily recall given it had been four years since I beat him (and on my first play as well), but I know my Samurott was quite resilient and had fighting spirit, and even with a worthy coverage TM being not available until postgame I still at least beat him thanks to Return spam iirc, because well it's the power of happiness.

and yay 28k posts as well

I basically used a Haxorus who Dragon Danced against his Configious, and then Dragon Clawed his Hydreigon when it got sent out. Otherwise, I think it'd be pretty tough to beat, hmmm. B2W2 was a little trickier, but, good ol' Flygon pulled it off!

My Expert Belt Emboar OHKO'ed or 2HKO'ed him with Brick Break, I don't remember it well. It was probably level 50 at that time.