Well it's very important to have your party fully buffed at all times in this fight.
Make sure you always have the defbuffs active (+70% physdef and +70% magicdef). Always renew them when they are at 40% or so.
Always hold Regen active with Nat and buff her accuracy.
It is very important to dispel his claws and Acrum whenever he uses this black ball attack. You should just dispell every buff from him ^^.
When he summons those dark robot soldiers justt kill then with Nat's Judgement.
The claws can be nearly ignored, just make sure you use enough areaspells to kill them over time.
When he summons his worms then apply 9 stacks of poison to both of them and Acrum and kill the one that throws blood at at you and poisons you. The other worm with the thorn should die from your poison.
Always attack Acrum with the element he is weak against. From time to time he changes his weaknes. When he does this he buffs himself with +50% attack or so. Just check his weaknes from time to time and change the weapns of Matt and Lance (you should have every elemental weapon (the weapons with 50% holy damage for example) on level 5)
Nat should wear The Pope Hat, the Pope Dress and Seraphim as weapon. This way she takes nearly no dark damage!
Lance should wear the Gas Mask (level 5 randomly summons Poison Gas!) and the Officer Coat (darkness resist).
For Matt the Officer Hat (dark resist and tank!) and the Army Jacket (Airstrikes!).
And always make sure you have enough to eat (>COFFEE!!!<, manareg and the stuff that heals the whole party).
Yeah those are just a few tips (perhaps other people wold do him with another strategy or so, dunno :7). Give it a few tries, Acrum is not that hard on normal, I'm playing on epic atm ^^.
Good luck!
( sorry for spelling mistakes or grammar :( )
