Rog3/Sorc6/Arcane Trickster10/AM1.

Spells to grab: Lesser Sonic Orb (1st level spells, Conjuration, so no SR, and Sonic damage, which is rarely, if ever, resisted), Sonic Orb (4th level version), Greater Invisibility, Gravebane, Golembane.

AM ability: Mastery of Elements. This lets you change out the flavor of your damage to whatever you want in case you run across something with an elemental weakness (burn trolls, for instance).

Why this works: Impromptu Sneak Attack. Even if they aren't flat-footed, they are now. Plus Greater Invisibility gives you Sneak Attacks against anyone who can't see invis. For those few who do... they are nailed anyways. Golembane/Gravebane lets you SA normally un SA'able opponents.