Hmm...you want an elven assassin? See if your DM will approve the Pathfinder version of Arcane Archer. The PF Eldritch Knight would be nice too, but isn't vital. Go Wizard 8/Arcane Archer 6/Eldritch Knight 6, and be sure to snag the usual gish abilities. Why does this rock, especially for an assassin? Ever seen a high level target in an AMF get hit by a Spell Matrix with 3 sanctum orb of X? No save/No SR/Works going into an AMF, and you won't miss with the Dex of an elf as an archer. You end up with 16 BAB/17 CL, 9th level spells, and are deadly at all ranges. Since you're an elf, you qualify for both Elf Dilettante and Areni Focus, allowing you to snag Hide and Move Silent, plus giving you access to every skill in the game. One spell later and you've got at least a +18+stat to the skill, and that's overkill by far. Wanna ramp it up a notch or two? In lieu of getting PF stuff, look up Build #8 of the Dragoon Handbook (currently on 339, but might be here too, Endarire's I believe). You assassinate by controlling the battlefield and then when the moment is right, leaping out of the sky and impaling your target with a polearm for dragonsplatting damage. Like, if you had a rod of greater quicken, you could one-shot the tarrasque as a matter of routine. Not to mention, polearm elves just scream royal guard, so it can even fit the fluff of now being a mercenary if you retired/got kicked out/killed the king because he was a weakling/etc.