The most efficient way to make a Shadowblade, who actually works on Tactician (keep in mind that Tactician isn't nearly as hard as people like to claim. It just requires you to understand basics of the game, namely crafting), seems to be to simply splash 3 Attribute points into Int and a single Ability point into both Aerothurge and Witchcraft. And then just treat the character as a standard Rogue with extra utility from there on.
Aerothurge 1 gives you Thunder Jump, for mobility, Avatar of Storms, for clearing stuns/causing a bit of non-scaling CC/protection, and finally Teleportation, for moving things around the battlefield, with the added benefit that you can safely use it mid- til' late-game on your own guys without causing any real damage, due to your mediocore Int.
Witchcraft is pretty much only picked up for the sake of Oath of Descecration. Altough the Skeleton minion is mighty nifty too. Decaying Touch being a great pick for the third skill, if you keep in mind that it might fail to be applied ever so often, due to said intelligence.
The 8 intelligence is there to prevent spell failure, of course.
A single point can very favorably to donated to the other caster skills aswell. But flavor is a thing and a Shadowblade with Bless and Rain just seems a bit off, being a Shadowblade and all.
Everything else is pretty much the same as with any other Rogue, really. Same talents, same skills and same stat-distribution. Discounting the small handful of attribute and ability points invested into casting, of course.
Also, don't forget to give your Rogue the Pinpoint talent. It's quite possibly the most powerful talent in the game as of now. Seeing how it basically counts as adding an entire school of skills to a character for the price of a single talent point.
The drawback with the Shadowblade, by the way, being that they don't really have the points to invest into Man-at-Arms. Which is a highly recommended splash for Melee Power Stance, Helping Hand, Battering Ram and the Slingshot talent.
But then again, warriors benefit a lot from splashing into Scoundrel as well for Fast Track, Walk in Shadows and Adrenaline, not to mention Pinpoint. So if you go Shadowblade, you can just have your warrior splash into Scoundrel/Marksman (Medic, Doctor, Treat Poisoning. Oh' my!) and get the Slingshot/Pinpoint combo, should you want it.
Which you probably do.
