The staple ability of the class is a suite of buffs they can provide which grant a wide variety of benefits. Each member of your party can have two such buffs per corsair. The way you grant a buff is to use the ability "phantom roll" which has a 1 minute cooldown. You pick one of your dice to roll (you have a die for every buff you know) and everyone within 8 yards gets a buff based on the number you rolled. Then for the next 45 seconds you can use a second ability "double-up" which rolls the die again and gives everyone with 8 yards a buff based on the sum of all dice rolled thus far. Note, this could be a different set of people if people have moved. Anyone out of range of the double-up keeps their initial value. The tricky part is you have a table of different results depending on the number rolled and if you ever exceed 12 you bust. People within 8 yards lose the related buff and the corsair actually gets a negative buff hurting that stat which they can't get rid of. This bust buff eats up one of your two buff slots so busting is pretty bad all around. Everyone else can still get 2 buffs but you're stuck with a bust. Bust twice and you can't even buff anyone else until they fall off. (All such buffs last 5 minutes so you can juggle 5 different buffs total.)
Different people are going to want different buffs (mages have no need for melee accuracy and beaters have no need for mana regen) so you need to get proper positioning amongst everyone in order to get everyone everything they want before they start fading. A lot of time is therefore spent running between clumps of people and dropping buffs on them. (Bards work pretty much the same way so the idea of having a caster clump and a melee clump is pretty common in FFXI.) Corsairs don't do awesome damage as a result of all the running around but supposedly they do pretty solid damage considering all the buffs they bring.
The first 20 buffs are all named after one of the 20 jobs in the game. Each such buff provides something that job tends to want (ninja roll adds evasion, thief roll adds crit chance, warrior roll adds old-school windfury, etc...) and actually gets better if the named job is in the party. Thief roll can add up to 19% crit if there's no thief in the group and up to 25% crit if there is a thief in the group. Everyone gets the bigger number, not just the thief.
The very first roll you get (at level 5 which I'm not even at yet but expect to hit tonight) is corsair's roll. This roll provides an xp multiplier for the group which is pretty sweet. (Especially when you're running a lot of MMM mazes since the multiplier stacks well with the winning chest multiplier.) So looking at things just for our group (we're up to 4 people with Byung having caught up last night) how do I maximize total xp% uptime? Busting is going to cost me 6% of my experience for 5 minutes and cause the group to have no xp buff for a minute. (I will actually get the second xp buff too but probably lose it when I give out a second buff to the group.)
First, the table for results assuming I don't re-roll this buff at all if it busts. If I have a 5 buff rotation already, for example, this will be the case.
The best result for this (and all other) rolls is to hit exactly 11. Unfortunately it doesn't seem like trying for an 11 can be right for this roll. You make very minor gains by rolling again on 6 but that's because only the corsair gets saddled with the 6% penalty. And as the corsair I'm not too thrilled with this deal. But the buff value of 12 (and consequently the EV of the previous rolls) isn't actually -1.5% because I can spend the next roll on xp again for the rest of my group. Busting again destroys my whole reason for existing (assuming the other buffs I provide are of any use and I'm pretty sure they're all insane) since I won't be able to put up a single buff for at least 4 minutes. I'll have to see how it plays out but if I try again I will likely sadle myself with 4 minutes of busted xp, 1 minute with both busted xp and buffed xp, and 1 minute with no xp buff at all. Refusing to double-up if it could bust a second time gives the following table (assuming a 4 person party and with the buff value normalized to a percent per minute):
So if I bust and buff again a minute later I expect the group as a whole to earn close to 11% bonus experience per minute. If my buff rotation isn't full (and with our current group I don't expect it will be) then it can be right to bust and keep going. (If I roll a total of 9 the first time, for example, the average experience bonus is only 8%. 11 is bigger than 8 and that's ignore the fact I have a 1 in 3 chance at a good buff for everyone.) Clearly the second time through I hit on anything below a 5 and never hit if I could bust. But what should I do the first time through? The final chart there, given the new value of busting, is:
From here I should hit on 1, 2, 3, 4, 6, 7, and 9. 7 is close enough that the selfish part of me wants to stay on it (and really since I'm going to be delaying a different buff by a minute by doing this is probably right anyway) but the rest of the hits are pretty substantial gains. Especially 9 where I'm gambling my experience in the hopes of giving everyone else a huge buff. Come on, lucky number 11!
For the curious it seems high level corsairs get a couple abilities to try to smooth out some of this randomness. Every 15 minutes you can fold which removes a bust debuff (or an actual roll if you have no busts). Also every 15 minutes you can force your next double-up roll to come out a 1 which is pretty great when you get stuck on 9 here, for example. Hit snake eye and move smoothly up the 10! (And how sweet is it to be playing a job with abilities named fold and snake eye?)
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