Katta is KOS to evil dieties, not necessarily evil races. If you worship Cazic or Innoruuk, for example, you are kos. Except for the invisible coterie assassins and undead, nothing sees through regular invisibility. I would keep see invis on so you can spot the assassins if they spawn (I believe there are 4 possible assassin spawn points, but they are rare).
I have seen level 40 pallys soloing in the graveyard, so I think that that might be a little too easy and too few spawns for a mid-50 necro. I have duoed in the bank area as a low 50 SK with a 50+ necro and you might want to look here for better exp. You will need to learn the pull pathing and fear pathing by trial and error. You can single pull the twin guards (there are many sets of 'twins' flanking the doors/arches at exactly lvl 57. Till then you'll need to initially split via dark/feign death. Once you have it down and the twins split, you can single pull continuously till you drop from exhaustion. Be careful exactly where you fear them, they can path in different directions (towards the courtyard) if you do it too close to the back wall.
There is only one roamer guard in the bank area, he comes out of the arch from the direction of the vendor house on the Twilight Sea side. He is on the same spawn timer as the guards.
Generally, we found this strategy to work best:
Pull one with darkness, take behind merchant building to far end, Fear and allow to path towards archway. If you can't kill in one pass, let him follow you back when fear wears off, and re-fear. You do not want to let him get to the archway or you will have adds. If you have low DPS, you will have to re-dark or he will run for the archway and it will be all over.
The people in the merchant building will not aggro you unless you enter the building... you can sit right behind the wall safely.
There is one other glitch in the zone you should be aware of: once every couple hours, the zone re-pops. If you are fighting at the time, that mob poofs and respawns with no aggro. All guards that are currently alive will re-pop. Dead guards will not re-spawn however, so you don't have to break the spawn again. You just lose the one you were fighting.
The guards hit (me) for max 117 and start going light blue at 58 I think.
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