Mouse sensitivity and volume adjustments are in the settings menu, available from pausing in-game. The mouse cursor is a bit of a weird one - the game and browser seem to be fighting for control of it. Pausing and unpausing fixes it, I find, but I agree that it would be preferable to not have to deal with.
The ichor is a part of the same shader used for rendering the terrain, with a splatmap determining whether or not the floor is lava. For the most part, it's a signed distance field, but I had to draw on top of it for some last-minute alterations.
As for the top... the tower seems to have a few cracks, doesn't it? Perhaps if you were to strike from really high up... ;)
Thanks for playing!