Euthanasia is real simple actually, she is there to teach you to use the cards. Right before her fight you get a card which you can equip to make yourself immune against her paralyzing attacks.
I must have missed a piece of collision by the lake, I will look it up.
This is actually rpg maker, I cannot code anything at all, and due to this some things just cannot be implemented. I have a plugin which can enable good fullscreen, but instead unfortunately makes fullscreen the only option.
I will port a fullscreen build tomorrow so people can choose. I almost always play it windowed. Diagonal movement is just a tick of a box away in rpg maker as well but I personally did not like how it felt, I have received mixed opinions on this.
Gameplay becomes a lot more advanced as you progress through the game but some general tips is that equipment setup actually can matter for individual fights, the moods and intentions get updated with new options as you make choices in the game, managing these things makes the system make a whole lot more sense I think.