Big Bang Build for my F/P

1st job - 67 points
10 mp increase
15 magic guard
20 magic claw
15 magic armor
7 energy bolt

2nd job - 121 points
20 spell mastery
20 meditation
20 teleport
20 slow
20 fire arrow
20 mp eater
1 poison breath

3rd job - 151 points
20 elemental amplification
20 explosion
20 poison mist
20 spell booster
10 teleport mastery
10 elemental reset
20 partial resistance
20 elemental composition
11 seal

4th job - currently 63 points
30 paralyze
1 meteor
2 big bang
20 maple warrior
10 magic mastery

Is the DoT they do enough to warrant using them while bossing? I'd think poison breath is not worth it since its base damage is also so incredibly low, but what about compo?

Poison Breath is not worth it. You'll just use Flame Arrow till you get Explosion and then Paralyze.
Poison is a terrible thing post Big Bang, not worth to max things for it, since Big Bang demands immediate training, the kind of poison mist, change channels and keep coming back is obsolete after that, when you're just hella powerful with explosion with a marvelous range.
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For Elemental Composition, let me tell you my opinion. For Ice mages, at all, Elemental Composition is definitelly not worth it. A reason? When you have a 140%x5 attack, why would you want a 480% damage single target skill? Not only that, but on the few situations you'll need a single target skill, Thunder Spear would be hella better than that. I'm saying this because of the experience i had with seeing some IL mages on KMS.
But FP mages seem different. They don't have two single target skills at third job, but two mobbing skills. Go for Composition, you'll need an 1x1 attack.

Poison Breath is not worth it. You'll just use Flame Arrow till you get Explosion and then Paralyze.
Poison is a terrible thing post Big Bang, not worth to max things for it, since Big Bang demands immediate training, the kind of poison mist, change channels and keep coming back is obsolete after that, when you're just hella powerful with explosion with a marvelous range.
.
For Elemental Composition, let me tell you my opinion. For Ice mages, at all, Elemental Composition is definitelly not worth it. A reason? When you have a 140%x5 attack, why would you want a 480% damage single target skill? Not only that, but on the few situations you'll need a single target skill, Thunder Spear would be hella better than that. I'm saying this because of the experience i had with seeing some IL mages on KMS.
But FP mages seem different. They don't have two single target skills at third job, but two mobbing skills. Go for Composition, you'll need an 1x1 attack.

Remember I'm not leveling through the jobs anymore, I'm already 4th job. Elemental composition would only be for a use every 10s for its DoT. Same for poison mist (but that one has been proven to be good for DPS already).

I know. You're in the same boat as me actually. I'm going to reset my skills but most of those i'll just put points into for the lulz. Because, i won't use seventy percent of the skills i'd put points into.
Go for it then, poisoning bosses seems nice tho.

Great build. I'll probably do the exact same thing til 4th job. Your build is optimal imo.

As for myself in 4th job, I'd go with paralyze first since that is the main attacking skill, then with any skills which significantly increase paralyze's power such as infinity,magic mastery, and MW; then I'd go with ifrit to increase DPM more, and throw in 1 meteor and 1-2 Big Bang for variety somewhere in between.

I’m currently parked at 138, which gives me 57 SP. This is what I’m looking at right now:

30 Paralyze (still need to find and pass Paralyze 30, guess I’ll be at Werewolves for a long time post-BB)
1 Big Bang (strong enough at level 1 for a long time to come)
1 Meteo (ditto)
10 Magic Mastery (a +30 matk bonus for 10 SP is a great bonus, and the added buff timer makes Ifrit bearable at low levels)

This leaves me 15 SP. Fire Demon seems to be a complete and utter waste of time with Mob-a-lyze around (and I honestly wish they had actually taken FD and Comp Arrow apart and changed the way they work so they remained useful somehow, as opposed to slightly upping their damage now and again and completely ignoring them otherwise), but having trained with Fire Demon and Elquines for a long time now I know how even a relatively weak Elquines makes things die noticeably faster, so I’m inclined towards using those SP to get 5 demon and 10 Ifrit just to get a functional Ifrit right away, as it would be otherwise several annoying levels of prerequisites and ineffectually-low-timer Ifrit. Afterwards I’d move on to do 19 MW (by lvl 145), then Meteo (lvl 155), finish Ifrit (lvl 162) before the low timer drives me insane (I've had Elquines at 65 seconds for two years now), then finally max Infinity (lvl 172) and Big Bang (lvl 182). I’ve no illusions about my ability to survive being dispelled at bosses to seriously consider going on most boss runs, so Infinity can wait.

As for DoT, I really, really doubt that anything more than Mist + Mobalyze is worth it, but I’m getting max Comp simply because I love the skill to death, plus max PR, at the expense of Seal. Comp’s damage being relatively close to Paralyze’s probably makes it worth it to use it for DoT, but I doubt that I would be able to remember to recast Comp every so often to renew its DoT in the middle of a heated boss battle where I can barely make out my character.

Now thinking about it, I'll probably take 9 points of seal and put them on PR. Seal will be pretty useless having a mobbing paralyze...

You can't use your points from 3rd job onto 4th job skills with Big Bang SP reset. :S
Neither the other SP reset from CS.

You can't use your points from 3rd job onto 4th job skills with Big Bang SP reset. :S
Neither the other SP reset from CS.

PR = Partial Resistance

Now thinking about it, I'll probably take 9 points of seal and put them on PR. Seal will be pretty useless having a mobbing paralyze...

Seal is quite useless for ANY (at least ok-funded) 4th job mages, unless some great monster comes along and needs to be sealed for survivability/anti-stun. That's why I'm gonna ignore seal as well; even though PR is not much better anyway.

As for late 4th job skills, I'm pretty sure Mana Reflection will still suck, and I'm guesing the same about hero's will. The least prioritized skilsl after those might as well be a high-leveled FD and perhaps a high-leveled meteor.

Best 4th job skills imo: paralyze, magic mastery, infinity, ifrit, BB
Good 4th job skills imo: MW, FD, Meteor
Bad 4th job skills imo: MR, HW