Inspired by Bostik's 4/13 video, I spent a couple days "progressing" and have currently downed 10 bosses out of 13 - and that's not the limit. Everything is done by a level 80 mage (fire), including trash (nobody has been inside with me on this lockout).
Here's my progress:
Siege of Ulduar
Flame Leviathan (normal)
Ignis the Furnace Master
Razorscale
XT-002 Deconstructor (normal)
The Antechamber of Ulduar
Assembly of Iron
Kologarn
Auriaya
The Keepers of Ulduar
Freya (3 keepers)
Hodir ("hardmode")
Mimiron
Thorim
The Descent into Madness
General Vezax
Yogg-Saron
Celestial Planetarium
Algalon the Observer (video)