Currently running a thief with psi and it's been the most fun I've had with a build. Interloper+10 is absurd. I'm at level 27, dominating, oddity mode, having just entered the deep caverns. While the combat has been rather easy, the build becomes very strong in that regard, the sneaking has been a ton of fun.
Build link.
This build definitely isn't optimal. I foremost wanted to make a really good sneak that was still strong in combat. Here's what I think my be worth changing.
- Metathermics isn't great. It's very good early on when Cryokinesis is your best ability. And Thermodynamic Destabilization is your way for dealing with crowds before you get Locus of Control. But after that it is rarely used. Maybe droppable.
- The build lacks a way to fight machines. The robot spam in parts of Expedition is nearly unbeatable in combat for this build. Fighting 8+ 700 health robots with near immunity to mechanical, heat, and frost damage just isn't possible. And the crowded rooms in some areas make sneaking very hard. It would be good to have a backup plan if caught while sneaking.
- Pickpocket was too high. I mostly wanted a peaceful progression through the Scrappers questline, to uncover the fat spy, and to steal back the thingy from that Hexagon guy. But as I was swimming in money, only the first two uses were very relevant. And last use only needed 100-110 anyways. I want to be skilled at Pickpocket because it's a "thief" skill -- it wouldn't be right to have it at 0 -- but that's a lot of points that aren't put to use.
- This build doesn't invest in mercantile until around level 16 or 18. It also doesn't invest in crafting until around level 22. Gear just isn't that great for much of the game. It would be nice to somehow invest in these skills earlier.
So, my thoughts are to drop Metathermics in favor of Temporal Manipulation. I also think Pscyhokinesis may be droppable down to 25. Without Thermodynamic Destabilization, there is less use for Telekinetic Punch, and Force Field doesn't scale with skill. Dropping Pscyhokinesis would allow investing in the crafting skills earlier. I think having access to Trance and some good headbands would more than make up for whatever damage is lost in the mid-game by not having Metathermics or Pscyhokinesis. Extra points should probably go into throwing for additional damage versus robots. Or perhaps traps to avoid metagaming certain areas. I don't know what to do about Pickpcoket. I'd rather find a few more good uses for it than decide to drop it.