Final Fantasy style "Blue Mage"?

[Herobizkit]

It is true that a Blue Mage would have a set limit to the powers he could 'steal', AND a limit to which powers he COULD steal.

To be fair, I haven't delved very deeply into the 4e monster list, but from a Heroic tier standpoint, stealing a Zone effect from a Firequench Wizard would be awesome.

In that respect, perhaps, like the Witch (and perhaps especially the Witch would be a great 'base' model), a Blue Mage amasses a (short) list of potential powers to swap during an extended rest. It would require a lot of cuztomizaton, to be sure.

 

[Fanaelialae]

Unless you want to throw 4e class balance out the window, this is feasible but would require a lot of work.

Some (or all) creatures would have an ability that the blue mage can learn. I don't think it should be more than one power per creature, as even doing one power per creature would be a pretty hefty amount of work for the DM. The blue mage also supports this, as I can't recall ever learning more than one ability from a creature.

The power should be based upon that creature's power, but would need to be rebalanced for use by a player class. Another thing to keep an eye on would be to ensure that powers with excessive synergy aren't available.

Unlike normal 4e classes, the blue mage's role would be that of a wildcard, largely or wholey dependent upon what powers he acquires. That sort of thing has both pros and cons.

It is doable though. My group ran a (heavily modified) 4e campaign a while back where we didn't really concern ourselves as much with balance. The DM introduced a blue mage-esque class that could only gain new abilities by acquiring them from enemies, which I ended up trying. It was... interesting. Definitely fun. My advancement was a bit out of step with the other characters, since levels weren't as important to me as what creatures I encountered. Sometimes I'd lag a bit behind, only to shoot a bit ahead after encountering a particularly tough (or synergistic) new enemy type.

 

[The Little Raven]

It seems to me that if any game will proerly use this concept, 4e is a likely candidate. Monster attacks are different enough from standard player attacks that they could easily be the focus of a whole class.

Or could they?

I wish I had some thoughts to put here, but for now, how might this be done?

I'd say take the spirit of the blue mage and adapt it in a way that works to 4e's strengths, particularly because the blue mage powers weren't always identical to the monster version anyway. Off the top of my head...

Controller.

Lore (feature) - +5 bonus to all Monster Knowledge Checks and bonus language.

Scan (feature/power) - Allows a Monster Knowledge Check, and grants bonus to damage against scanned creature until end of encounter.

Draw (feature/power) - Grants access to all at-will powers from power lists associated with the monster's determined origin/type/keywords. Allows you to pick an encounter or daily power from the power lists associated with the monster's determined origin/type/keywords.

Power Lists - Have several lists based on origin (natural, immortal, fey, etc), type (humanoid, beast, animate, etc), and keywords (fire, dragon, undead, etc) that blue mages can choose from. You can also create some custom scaling ones for iconic FF creatures, like cactaurs and 1,000/10,000 Needles if you wanted to go that route.

Powers - Their powers are empty slots that they fill when they choose one to use from the power lists after Scan.

From there, you can decide whether you want these to be learned powers (with a Spellbook-like ability that allows you to swap during rests, but you have to scan and use from the list before you learn it) or is limited to the powers only from lists available during that encounter for a spontaneous-caster type of deal.