Few things.

Not sure if these have been posted or not, they weren't in the known issues or in the first three pages of bug reports.

In the Cathedral, when skeletons are climbing the wall and jumping through the windows, if you hug the top wall where they're coming out of, the skeletons will disappear and not be attackable by the player using non-AoE mouse clicks. The Templar can still attack them, so it would seem that this is entirely a visual issue.

Secondly, I forgot where exactly, but there's a locked gate that you can attack the lock constantly and for the most part, do nothing too. However, I noticed that the Wizards Magic Missile attack can break the lock and open the gate, which then greets the player with an invisible wall.