[awall]

Don't get your hopes up. It doesn't exist. There's no "super secret" blue mage class, there's no hidden character who learns monster skills, nothing. You can get monsters in your party, but that's it.

It is theoretically possible to hack a Blue Mage into the game via a gameshark. If anybody's interested, I could go over how to do that. I don't have the gameshark to do that, and even if I did, I'm not sure I would; it'd take a helluva lotta work and I'm sure there'd be a lot of kinks that'd have to get worked out.

Also, there's the issue that a Blue Mage would either be incredibly good or incredibly bad. I'm not sure how many people pay attention to monsters' stats, but you'll notice that they typically have ridiculously high MA; the reason for this is to balance out the fact that damage formulae for monster magic are laughably bad! We're talking stuff like... well, Thunder Soul (Skeleton) does MA * 2 damage, Mimic Titan (Sacred) does MA * 3, etc. To compare, Fire does MA * 14 * faith_multipliers which, assuming the caster and target both have 60 faith (which is fairly crappy... mages should typcially have around 70 faith) is about MA * 5. Fire 2, Fire 3, and Fire 4 do MA * 18, MA * 24, and MA * 32 damage (times a faith multiplier) respectively. The short version of this is that beyond the very beginning of the game, black magic will do significantly more damage than monster skills. To compensate for this, you could jack Blue Mages' MA up to what monsters have, but then that leaves potential for abuse; a Blue Mage who equipped Black Magic as a secondary would cause absolutely obscene amounts of damage with his Fire spells and never use Blue Magic at all.

Having said that, I'm now going to throw it all out the window and pretend there was a Blue Mage class. Pretend that the class existed and somehow had their stats set so that Blue Magic was reasonably powered compared to other jobs. What skills would you give to a Blue Mage? Remember to think about a few things:
1) Blue Magic is free (it has to be, because monsters have almost no MP) and requires no charge time.
2) In order to learn a monster skill, the Blue Mage needs to get hit by it. Since monsters are smart enough not to target beneficial abilities at your characters, you can only learn beneficial abilities that have an area of effect (the ability isn't targeted at your Blue Mage, but he can get hit by it anyway).
3) Demons are not monsters. This means that Dark Holy, Lifebreak, Ultima, and Nanoflare, are Dark Magic and not Blue Magic. Sorry. (Giga Flare, Hurricane, and Ultimaguest, however, are in the Behemoth Skillset so they could be learned).
4) Also, some of these attacks may be really hard to learn, because you need somebody with Monster Skill to be standing next to a monster to allow it to use certain attacks against your blue mage.

Anyway, without further ado... here are the 10 abilities I would give a Blue Mage:

-Choco Cure - (Heal MA * 3 HP.) Yes, it sucks. Yes, it's hard to learn, because you either have to charm a chocobo or make it desperate enough to use Choco Cure despite you standing it the area of effect. However, it's the only healing monster skill in the game, so I feel Blue Mages should be able to learn it.
-Goblin Punch - (Do maxHP - currHP damage.) Interesting damage formula and a traditional FF blue mage skill.
-Selfdestruct - (Do maxHP - currHP damage, area of effect). MASSIVE area of effect damage and another traditional blue mage skill. Actually, it's just like Goblin Punch, but with area of effect.
-Drain Touch - (Drain target_maxHP / 3 HP.) Drains 1/3 of the target's HP!!! That's better than the Oracle's Life Drain! Use it on Velius and watch him cry as you eat over 500 HP.
-Choco Meteor - (Do MA * 4 damage.) Not wonderful damage, but 100% accurate and long range. Sorta like Geomancy, minus the status or area of effect.
-Cat Kick - (Do PA * random(1..8) damage, 50% chance of knockback.) Simply because knockback is fun.
-Mindblast - (MA + 35% chance of causing Beserk or Confusion.) Anybody who this has happened to knows how good it is. I think you can still learn a monster skill even if you're confused or berserked.
-Wave Around - (Do about PA * PA / 2 damage to anybody next to you.) Simple, easy to learn area of effect attack.
-Giga Flare - (Do MA * 7 damage to an absolutely ridiculous area of effect.) Okay, this attack would be good even if Blue Mages didn't have turbocharged MA. Do you know what this hits? 4 panel range and 3 panel area of effect. This is positively brutal. In theory, it's hard to learn because you can only get it from a Monster-skilled Behemoth; however, if you take a blue mage with you to the Velius fight, one of the Archaeodemons will cast it at some point.
-Triple Flame - (Do a whole truckload of damage... three times!) This is your reward for taking a blue mage to the final dungeon. Learn it off one of Balk's Hydras and then massacre Altima with it. Sure, it's overpowered... but that late in the game you already have Orlandu, Reis, Chantage, Deep Dungeon equipment, Calculators, etc.... adding one more overpowered attack won't change that much.

So, what do you think a Blue Mage would have in FFT?