Fluff is cool.
Broken Mind-This is worded oddly. What do you mean by both spirits taking damage? You're still one character.
Driven Out-That's a little too powerful. If I'm reading it right, (and I might not be, it's kinda poorly worded) you get something with an 18+ your Dexterity mod in Dexterity. So let's assume you have a Dexterity of 14. That gives it a Dex of 20. That means it's hitting at +8, the same as a Fighter, with two attacks, the same as a Fighter, and deals 2d6+8 damage, even better than a Fighter. And this is a bonus action every short rest?
Even if it just has a Dexterity of 18, it's still +7, two attacks, and 2d6+7. That's basically as good as a Fighter (trading a point of accuracy for two points of damage.)
I take back what I said-it's not a little too powerful, it's really overpowered. This needs to be toned down a LOT.
Two Ways To Slay-Add in the detail that they are cast at spell level 1. Then I think this feature is okay.
True Self-This seems really weak. It's a big penalty for a paltry bonus. The advantage on Intelligence saves is nice, but still really weak.
Broken Mind-Needs to be clarified, but seems okay.
Driven Out-Needs to be toned down a ton.
Two Ways To Slay-Needs a minor bit of clarification, but should be good.
True Self-Needs a major buff.