Let's see... Iron Golem in Sen's Fortress, Dark Souls.

100% chance I survive since I'm rolling with Black Iron Tarkus. Guy's a bad ass.

Summoning?
*meow meow*

That was a boss? wow...

Giant fruit-eating frog in Okami Den ... I'm fucked, unless someone has an extra painted dog with a magic paintbrush and a sword laying around. 

Velstadt, The Royal Aegis (Dark Souls II)
Yeah, I'm screwed... No way I could punch through his armor, lol

That weird alien General Skun-ka'pe in The first episode of Sam & Max: The Devil's Playhouse, The Penal Zone. Given he was fooled by a potted plant I'm sure I could take him down no problem.

What? Stop looking at me like that!

SInce I can't remember, I have to go with: I am soooo dead!

I guess for me it would be a psychoatic tree from realm reborn, im quite possiably fucked.

Umm...none. Considering its the last boss from Shadow of the Colossus.

Well I have been playing Gran Tourismo 5. So other than getting ran over...lol. So I will have to cheat and go with the day before. Fighting Bad Ma and his Merry Midgets at the entrance to the Bloodshot Strongold in Borderlands 2. Well all I can say is I'm no Vault Hunter, but I play one in a video game. Yeah, he would stomp me.

It's Smorg from Paper Mario Thousand Year Door, but unless I can conjure a giant star under my feet to create a giant earthquake, I'm finished.

Since Tony Hawk Underground 2 doesn't have bosses, i'll roll with Hotline Miami. It's with the black security guard and given that it's a one hit kill with punches, i've got no chance of surviving.

Edit: Oh wait, you meant last boss. Then I don't know.

Final Boss?  Heck no, unless I had a Fire Magic...  Mezlas from Alundra.

Regular old boss?  Probably, if Tidus can do it, so can I.  Something from the early stages of FFX.

F-f-final boss?

Jubileus, The Creator from Bayonetta.

I'm fuuuuuuucked.

Last boss I fought was Bowser from Yoshi's New Island.  Yeah I don't think I'd do too well.

Although I've watched over Bowser's kids a few times, so we're on pretty good terms. :)

None.

Since all I've been playing is fighting games online as of late, I would say maybe 50/50. Depending on how fucking laggy its going to be.

Taurus Demon from Dark Souls? Well I did beat him by tricking the guy from jumping off a bridge, so I'd say if we fight anywhere he can fall off, I stand a good chance. Only problem is there's no way I can leave there without something killing me.

Last boss I beat was a ginormous cheep cheep in Paper Mario: Sticker Star. So yeah, it would probably just swallow me or something.

Coveteous Demon from Dark Souls 2 (haven't played in days) 100% survival because the guy is fucking retarded.

Last boss I took down was one one of the gang bosses from Crackdown. Minus his weapon he was weak, and if it came down to a street fight, I like my odds.