Your about to fight a boss and you can summon two allied Champions to assist you, who are those Champions and why?
Since he can summon even more back up
BECAUSE SHE TURNS INTO A GOD DAMN DRAGON!
or
She's got stuns and moves very quickly so she can avoid the bosses attacks.
She can use Tibbers to tank for us.
Now who's ready for a little http://27.media.tumblr.com/tumblr_lt9tjrgETZ1qi9qvfo1_500.png !
so many reasons
he can immobilize the boss
he can deal meaningful damage to the boss
he can speed us
he can revive us
And before the boss fight... HE MAKES GRINDING 8% MORE EFFICIENT
because he is a spoony bard who gives us +4 charisma and +3 strength
+ 
They wouldn't even be able to move ;D
+ 
There wont be beating this team.
Uh..... it's hard to pick because I have absolutely no skills. I'll assume I can choose a weapon, so I'd probably choose a bow and be an adc So
Tanks the damage, keeps the boss locked down, and we all PRAISE THE SUN
Healer and such, Kayle seems pretty good for that. And she seems pretty willing to praise the sun, too. Plus, she'd be able to deal tons of damage (no pun intended. No, seriously)
Outheal them and then crush them with stars
and 
to overrun the boss with sheer numbers
and
to make him squishy and troll him...HUE
And 
Puns of damage + Cho'gath to tank
And I don't know many people who would want to fight those things
