Favorite optional boss

[Mr. Omega]

Inspired by a list of a similar name. Pretty simple concept, so here are mine. Keep in mind, I have't played that many games with optional bosses, but I want to see other people's choices.

Red from Pokemon Gold/Silver. Yes, he is optional. But the game encourages you to go fight him, making it seem required. But it's one hell of a fight, even more so in the remake.

Edgar Ross from RDR. A bit of a stretch here calling him optional, considering you need to kill him to see the end credits, but the mission is the same structure as a side mission. Still, the fight against him was standard, but it just felt so satisfying to fill him with lead...

Queen Zeal from Chrono Trigger. Once again, kinda pushing it calling her optional, but honestly, Lavos itself is an optional boss until the very end, and you can skip the Black Omen ship. The better way to classify Zeal is an optional stage in the end-boss. Still, Zeal put up a good fight. But this fight will lead directly to the end-boss, so you better be ready!

Culex from Mario RPG. I have a lot of personal memories involving this boss when I was young. Tougher than the end boss, but actually possible to beat at the first possible encounter with the right items and strategy.

Bonetail from Paper Mario TYD. It was a pain in the ass just to get to this boss, and heaven help you if you lose.

 

[Ashcrexl]

Sephiroth! best optional boss ever! his array of insanely cool and punishing moves combined with one-winged theme made him the best optional boss ever!

 

[dancinginfernal]

Red from Pokemon Gold/Silver.

This, it was such an epic battle.

Sephiroth! best optional boss ever! his array of insanely cool and punishing moves combined with one-winged theme made him the best optional boss ever!

I'm assuming you mean from Kingdom Hearts. Otherwise, I have issue with this.

 

[shogunblade]

Sephiroth from Kingdom Hearts 1 and 2, just so you can say you could in the first one, and so you could unlock the awesome keyblade you get in 2.

Culex is another awesome boss, as you previously mentioned.

 

[Sarah Kerrigan]

Sephiroth in Kingdom Hearts II in particuler. I tried everything I could and actually beat him in under 48 hours. Best optional fight ever.

 

[Misho-]

Sephiroth in Kingdom Hearts 1 and 2, although he was tougher on the first one... No quick time events... MAG/LOM

 

[Mr. Self Destruct]

that sand one with multi arms in kingdom hearts one, good times

 

[Colonel Alzheimer's]

If Edgar Ross is optional, then every other fight in Red Dead is optional too. The game doesn't force you to kill anyone, you could just wander the West without doing any missions, if you want. But whatever, it doesn't really matter.
OT: Red from Pokemon, and I can't think of anything else...

 

[WhiteFangofWhoa]

The twin Doppelgangers in Castlevania Portrait of Ruin, located at the bottom of the Nest of Evil. As far as I can tell, they can use pretty much every weapon and ability you can equip, or at least the Charlotte clone can. All that was missing was Dual Techs, but that might have been a bit unfair since they have unlimited 'MP'. Plus, in order to reach them you had to fight all the coolest bosses from Castlevania Dawn of Sorrow along with the usual barrage of hugely powerful optional foes.