This is Wotlk level 80 Instance: Naxxramas, Spider Boss (10 Man, Non-Heroic)
This boss is very easy with 2 tanks (MT and OT) and atleast 4 healers, and the rest DPS.
After you make yourway through to him have the MT and 2 healers circle him around the room.
Have DPS keep DPSing him until he summons a Crypt Fiend.
The OT and the other 2 Healers and the DPS'ers go and kill the Crypt Fiend ASAP. (waiting to long will have him continue summoning more and more Crypt Fiends)
Around 85% he will use the spell "Insect Swarm"
Who ever has his aggro continue going around in the circle until he dies.
Rinse Repeat.