Pentaclypse and Ultaclypse are the same mobs. So it really does not matter which you decide to banish. The strategy remains the same for both of the named.
Pentaclypse comes complete with 4 Epic x 4 adds that when killed make the Void Beast (Penta/Ulta) stronger. A typical strategy is to pull the adds to a secondary OT spot while keeping the Beast near the center of the room. You dont want to start the fight by moving the Beast too much because he hits very hard and very fast.
Many raids will kill two of the lamia encounter adds and then offtank the other two with either a Paladin or Shadowknight or both. The lamia's do mem-wipe so be sure your OT tank has good AOE aggro ability.
Thats the first part of this encounter. Have your raid practice getting the seperation part down.
The second part is killing the Beast while still OT'ing the adds the entire fight. The Beast will cast Nether Cloud which is the same Noxious AOE that you encountered with Absatalious just prior to Tythus. So you should be rather familiar with it. Only this time its gonna be very deadly to the MT if not taken care of in a certain manner.
The Beast has a damage shield on him that when proc'd will make the attacker immune to all beneficial spells. So if the AOE is incoming and the damage shield is proc'ing on the MT, you are gonna have problems healing and curing the MT. You need to have your MT stop attacking the Beast when the AOE is incoming. You will know when the AOE is incoming when the Beast is casting a Black Tornado around him.
Try to use only massive damage spells during this fight and dont put damage shields on the MT that could proc the Beast's damage shield right back.
Debuff Pentaclypse ASAP and you will more than likely need to have 4-5 healers on the MT at all times your first few times until you get good with the encounter.
Keep the encounter adds in place with the OT and you just have to worry about damage on the MT and curing that Noxious AOE. Call ins and outs for the Stunning Blaze AOE which has nearly a 53 second recast timer.
Drop Pentaclypse and then finish off the adds. Grats on loot!