Oath of Vengeance. Fits with Gityanki being LE. IMO.
For the love of all that is holy - the psycho Minthara was a Paladin of Llolth, then a Paladin of Absolute. And if you recruit her she is a Paladin of ... something.
So a Paladin of Vlaakith (or some other Gityanki thing - Tiamat, Orpheus, Bahamut, Scratch etc.) is not outlandish. For the Evul! feel you can go Oathbreaker 3 minutes out of the Nautiloid. You'd have to endure the dialogue with the Scottish guy, though ...
As to the Dark Urge side - that's up to you
