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A reflavored monk 1 or 2/warlock x with a Warlock's Scepter and a familiar who goes into the item-based classes from UA would make a pretty solid magical girl. Better, arguably, than the 'companion is stronger than the PC, not to mention 'balance' was not one of our concerns' BESM version. A straight warlock seems a little light on martial power, though.
Wildshape (transformation sequence), and Animal Companion (get a raven or something that can talk) and wham, all necessary flavor met, or even go MoMF and use Obtain Familiar as a feat.
Plus, Druids have Wild Empathy and a few other things that follow in line with the Magical Girl phenomena.
Arrrr, me eyes! This thread must be from the bottom o' the sea.
You scurvy dog be takin the warlock - fearsome looter o' the seven seas, with a cutlass of pure witchcraft and in leage with' the devil himself, doomed to go to hell - In other words a real pirate! - and turn him into a landlubber! We should be sendin' your ship to the bottom o' the sea for that, matey.
And don't be gettin' me thinkin' about tharr Barbie movies at all.
You guys are forgetting that they need a feat or class ability that allows them to join hands in a circle, chant a phrase, and unleash a huge bolt of energy to take out the BBEG! Also, the magical transformation has to give them the ability to change sexes as well as shape.