At the GM's behest, I'm taking my level up mid-combat, since I started the session so ridiculously close to level 3.
My choices for a second lvl1 mystery were:
-Carpet of Shadows, one 5' space of difficult terrain per caster level. (Not great)
-Voice of Shadow:
Command, or Daze a Construct or Undead. (the DC would be 12, so not great)
-Bend Perspective: Peek around corners, can be moved once per caster level at 10' per round. (I can Hide in Plain Sight and carry a Dark Lantern, so nah.)
-Dusk and Dawn: Either Darkness or Light spell. (I already have a Dark Lantern, and why would I need Light?)
-Mesmerizing Shade: Will save vs. Daze, -1 to attacks, checks, and saves on failure. (not bad, but I'd almost never actually get to Daze anyone)
-Life Fades: 1d6 nonlethal damage per level. (the correct choice, since I have Reach Mystery, making this my strongest attack... 3d6, at range, if I can sneak attack, which I typically can since I can sneak all the damn time. Plus, we fight a lot of nobles, who make better hostages than corpses. On top of that, I intend to take the other two mysteries in that path eventually, which means I'll get a bonus metashadow feat later.)
As for my feat...
-Weapon Finesse is pretty standard for anyone with Sneak Attack, but it would only be a difference of +3, and only when using my rapier. Still, I'd become a bit more CQC-capable.
-Craven fits my character... a bit... and more sneak attack damage is good, but it's not super great.
-Darkstalker is rather situational, but fits my character well, and could potentially save my bacon against monsters with esoteric detection powers.
-Maximize Mystery could be handy (since the Random Number God seems to have decided that I'm good at stealth and spellcraft, but not dealing damage), and would allow me to take Quicken Mystery later.
-Trickery Devotion is a good one, since I'd be able to bluff enemies for sneak attacks...... once I hit level 5. I think I'll take that one at level 6 instead.
-I can't even use Umbral Shroud until I hit shadowcaster level 5...
I think I'll take Maximize Mystery. In terms of flavor, Eosri's fighting style involves taking enemies down with precise attacks from the shadows, but lacks the physical training to do it with weapons alone, and compensates with his shadow powers. Mechanically, this means that all I have to do it hit people with a sneak attack for 18 nonlethal damage- not bad damage on its own, makes it reasonably easy to take hostages, and they won't blow up when Lawbringer finishes them off (unless he gets a really, really epic kill). Besides which, when I get the Umbral Touch mystery, Maximize Mystery will apply to every attack I make with it... which is to say, several attacks, each of which is worth exactly 30 damage, plus potential sneak attack.