Tank
Focus on doing as much threat as possible on the boss, so the DPS can go all-out. Maintain threat to avoid [Distracting Pain] debuff from being applied to other party members.
Note that after Sneed's Shredder crumbles, Sneed will appear and have a new threat table. [Taunt] Sneed and get as much threat as you can on him. Sneed casts [Disarm] , so be ready to use abilities that don't require a weapon in order to maintain threat.
Damage Dealers
After Sneed's Shredder crumbles, focus on dealing as much damage as possible to Sneed.
Healers
This fight is a tank and spank so you should focus your healing on the tank.