-ninja 2 (to get 1d6 sudden strike and ghost step, which works like improved invisibility according to FAQ)
-fighter X + Martial Stalker so your fighter levels stack with ninja levels for ki points, to let you ghost step more, and gives you an AC boost.
-Drow of the Underdark variant fighter loses heavy armor prof, and tower shield prof and gives you +2 initiative and Dex mod to damage vs flat footed opponents. Alternate class features have no prerequisites,(unlike substitution levels) so you dont have to be a Drow.
-If youre using pathfinder at all, use the pathfinder fighter, and grab the pathfinder crossbow Fighter variant from the advanced players guide to get 1/2 your dex mod to damage again.
-Use Crossbow Sniper, the feat from PHB2 to get 1/2 dex to damage AGAIN.
-At some point, dip into Pathfinder rogue and use the Sniper variant (also from the APG) to half ranged penalties and get another d6 of damage against flatfooted opponents.
-Once all this is set up, go into some PRC that progresses sneak attack with a decent BAB.
do basic sneak attack buffing things, like getting magic items that enhance it (bracers of murder) and taking the craven feat from champions of ruin that gives you a -2 fear saves but gives you a +1 PER CHARACTER LEVEL to sneak attack damage. Dont forget to focus on your crossbow feats, getting things like rapid reload, rapid shot, and if you want to use a heavy crossbow there is crossbow mastery from the APG. Also the PHB2 has deadeye shot or something that lets you ready an attack for when someone else attacks the target to count it as flatfooted, which will be useful when you EVENTUALLY run out of ghost steps.
