(Hopefully someone didn't make a topic of this already)

The bosses for hardest can be anytime through the game.

The secret boss are basically bosses stronger than final bosses like sephiroth or Terra. (for those of you who didn't know)

Hardest: sephiroth, Terra, Nebilim (tales of the abyss on unknown not fun).

Also Raidou kusunoha in devil summoner  soul hackers (he is a douche.)

 Elizabeth from p4 arena score attack mode yes in my opinion it's hard as rocks it counts for both hardest and favorite secret boss because getting to her is a journey it self.

Favorite: Mr.Hanekoma  ( Live in the moment) Elizabeth from persona 3. 

 

So what are yours?

( Side note sorry for rambling on so much this time will try not to in the future)

Hardest (Not counting secret/optional bosses because those would obviously be here)- Sho Minamimoto (The World Ends With You), Pkmn Trainer Red (Pokemon Silver/Gold/Crystal/Heartgold/Soulsilver)

 

Favorite optional bosses- Ultimate Noise (TWEWY), Mysterious Figure (Kingdom Hearts: Birth by Sleep)

Hardest bosses

Nicole - Dead Space 2 on Zealot and HARDCORE

Xemnas Final Form - Kingdom Hearts II

Almost all Bosses - Eternal Sonata

ALL BOSSES - Lost Odyssey

 

Favorite Bosses

Handsome Jack - Borderlands 2

Nicole - Dead Space 2

Gamabuta - Naruto Ultimate Ninja Storm

Succubus - DmC : Devil May Cry

Metal Kor - Jak II

Tiger, Dragon, Eagle, Cobra - Psychonaunts

Alex Mercer - Prototype 2 (Disappointing, But fun kicking his butt)

 

 

There's not really any games that have optional Bosses... So yeah...

Hardest bosses(on hard difficulties):

Terranort - KHBBS

Xemnas Final Form - KH2

Tabuu - Super Smash Bros Brawl

Chaos - Dissidia Final Fantasy

 

Favorite Secret bosses:

Kurt Zisa - KH

Phantom - KH

Hardest Boss Battle: Adamtortoise(Final Fantasy XIII) and The Guardian of Worlds(Ni No Kuni Wrath of the White Witch).

 

Fav. Secret boss battle: Lingering Will(KH2FM) and Sephiroth(KH1 and KH2).

Hardest boss: Evrae (Final Fatasy X) That boss I was furiously frustrated,  I never beat him.

 

Secret boss: Vanitas' lingering Spirit (Kingdom hearts BBS) I was this close to beat him once but he manage to defeat me, yep he's one touch sucker.