I find the upgraded skills don't always work, and seem to override one another. For example, if I upgrade the obliteration beam so that I can move, and then upgrade something else, then I can't move. If I upgrade the Arcane Missile to be blue rather than purple, and then I upgrade it to have remnant missiles, I get the remnant missiles, not the blue orb. If I remove and replace the blue orb option, I lose the remnant missiles. Nothing in the text says this should happen, and I don't see people on Steam complaining about it, so it's either GOG related, recent, or it's something with my specific install. It's driving me batty, too, because now I'm not sure what's actually active and what isn't.