Pretty much any of the MtG novels that focuses on a Planeswalker, at least before the latest update where they nerfed the Walkers to hell and made everything piss and fail.
The 'old' (and by old I mean anything before the latest update, also known as 'real') Planeswalkers were immortal shapeshifting supermages that spontaneously occurred in normal people for no readily apparent reason. They could tap the fundamental forces of magic itself directly, gaining effectively infinite power that is only curtailed by how much of reality they control (and are thus tapping for power) at once, and the ability to travel freely between all dimensions. And they're immortal. And they can look like anything.
To give you an idea of how powerful these bastards were, the Planeswalkers were the in-universe explanations for what the people who played the card game MtG were. The players freaking existed in the MtG universe. They were the Planeswalkers, and the card games were supposedly epic-scale conflicts between opposing Planeswalkers who conjured up armies of disparate entities from across the multiverse to do battle in their name, for whatever personal or trivial reason the Planeswalkers were doing it that day. Sometimes, it was to stop a great evil, or prevent universal collapse. Sometimes, it happened because the Planeswalkers were bored. Gods exist in MtG, but they're mostly an irrelevant footnote, because the Planeswalkers were much more directly involved, arguably much more powerful, and far more relevant to the direction and fate of the MtG universe in general.
Then the new update changed Planeswalkers from "the players" to "hero units in the game," and as you can readily expect, going from "the thing playing the game" to "one of the pieces in the game being played" is a humongous nerf, both in terms of cosmological position and in terms of personal power.
[EDIT]
Goddamn your ninja, Genocide. Fine. Most of the EU novels that deal with the Skywalker kids have them being ungodly powerful. Whatshisface basically became Buddha for about three minutes, but then gave it up for unspecified emotional reasons (read: he's a giant pussy).