Tier 2 bosses, contrary to tier 1, generally require a specific group makeup. You definitely need at least 1 tank, 1 priest, 1 enchanter, and maybe 1 druid.
All t2 bosses have aoe damage effects as well as high damage on tank, and adds, necessitating the need for buffs provided from chanter and priest, and aoe rain from druids.
Below a certain %age most bosses will enter desperation, causing more damage with higher accuracy. During this time it's important to burn them down.
T2 boss drops generally require a higher level, from 95 to AA10.