Geocide, are you talking about the FG access or the Necromancer class quest? For the FG access the last part is in an instanced zone with tons of ghost mobs in it that are roughly lvl 14 I believe. Then there are the boss mobs that are located either upstairs or downstairs and require no spawning technique. Just march on up there and kill them. Once your done head back to the entrance, talk to the npc, pick a helmet, and your done.
For the necromancer class quest last fight it is also in an instanced zone. However, this is a solo encounter in which you can not bring friends with you. This is the one where examining a desk spawns the boss mob you must fight. If this is the quest you are doing then yes, absolutely clear the entire tower before touching the desk. Once the tower is cleared tell your pet to stay on the bottom floor while you run up and touch the desk. Then run back down, tell your pet to attack and immediately stun him. That should guarantee an easy, quick battle.