135 NL Never killed Zakum in GMS. How much damage should I do before going on a run? Also do I use onyx apples? How many would I need per kill? Can I get helms as a DPS? I have one but would like to try scrolling one.
Your range should be at least 3k clean in order to do "decent" damage at level 135. Also, do not join a run without Sharp Eyes because that would decrease your damage dramatically at lower levels. Maybe when you're ~160, SE wouldn't matter as much but for now, always run with a bowmaster or marksman in the party. I recommend appling at arms so that it'll speed up the process and you can also white and/or gain more experience. Other normal attack potion like warrior elixir or energizer is good for the body. I only need 2 apples at most for zak, generally one for arm which should last a little bit into first body because of how OP alchemist is and another apple for 3rd body because you wanna try to outDPS others for that extra exp. If it is not a "sales" run and simply exp, the attackers are welcomed to reloot, just need to announce it before hand so that you don't get left dropping your helm and then someone else taking the last helm (cough I cry still cough). Good luck with bossing! You should also try krexel because that's a great chunk of exp.
The upper limit of your attack should be at least 3k without any attack potion or buff. Krexel is so much easier than zakum because you only have two high HP target (250 million HP each). You get hit for ~2.2k magic damage and most of the time, will just be standing at one spot spamming Triple Throw. It does, however, take longer because most people just go with a duo or trio instead of a full five attackers party.