Arbitrary invisible clips on erbium
The hole in the first picture is completely clipped, part of the rock in the second one as well. On one hand it's very hard to push someone out of the map because most likely he be stopped by one of the clips, on the other, once outside you have to keep in mind which "open" areas are in fact invisible walls if you wanna get back in. This feels very cheap, not to mention how annoying it is.