Which boss battle was the hardest in the pokemon games?

[Red and Blue]

From the games I finished to completion definitely Volo. It's a 6 vs. 8 so already the battle is rigged against the player. Especially since you aren't given the option to switch out after beating a Pokemon. Easily my hardest trainer battle.

I might of struggled with Necrozma if I didn't get a critical hit with Decidueye's Sinister Arrow Raid.

 

[TwilightBlade]

None of the trainers in the poll were hard for me to beat. I actually had a much harder time beating some of the Totem Pokemon instead like Totem Ribombee. :[

 

[GarchompTheAssassin]

The only one of those I remember struggling against is Ghetsis and his illegal Hydreigon in Pokemon White.

 

[Captain Jigglypuff]

Ghetsis In BW is pretty hard considering you fight him immediately after N and the E4 and you don’t get a chance to heal. Cynthia is also pretty difficult mostly because of her Spiritomb being able to absorb hits and it taking two hits at minimum to KO it unless you have something at Lv 100 with a Fairy type attack.

 

[masdog]

From the games I've played so far, I'd say that Cynthia in Platinum was the hardest traditional Pokemon Boss fight I've faced. Spiritomb was an absolute monster.

The overall hardest was Arceus in PLA. Part of it was getting the timing down, and part of it was due to using a Switch Lite. I didn't make any progress in that battle until I paired a Pro Controller to my Switch and used that instead of the built-in controls (but that had other problems, mainly needing to prop up the Lite to avoid neck pain...)