Thank for your thoughts!
Yeah I'm hoping that the latching on enemies won't be annoying but it's very possible...
Good question about the souls. I was thinking that you would keep unspent souls until you die. That way you can save up to spend on more expensive upgrades. Something I haven't decided on is that when you complete the hard ending, Tress still wants all those souls. Does she just hope you spend them all? Or take them from you? Or offer to take you home in exchange for your remaining souls? Because in my mind, Tress needs all the collected keys and all the souls to be freed.
I'm thinking I'll keep the design doc as it is and use side notes or something to fill it out or make changes as I find them necessary. That'll be maybe an interesting study from concept to reality.