What Was Your Single Hardest Battle in the Pokemon Games?

[Bellus]

Ghetsis destroyed me. I went in that battle with 30 revives and came out with 2.

It was his Hydreigon... That thing was horrible.

 

[Xenidal]

Whitney's Miltank in Generation II (don't remember if the re-make was also difficult).
Also, that ice gym leader who had that Dewgong or whatever it was that kept using Rest.

Other than that, Cynthia in Black. Because she keeps evading everything and my Pokémon's levels were probably not high enough (I eventually beat her by using my level 100 Arceus... cheap win...)

 

[Blue Flare]

I have been playing Pokemon for years without having much trouble, but Alder in Black was by far my hardest the first time. All of his pokemon were easy to defeat until Volcarona, who, when combining bug buzz with quiver dance, managed to OHKO almost my entire team.