It is possible to jump on top of hostile creatures in combat
It is possible to jump on top of small hostile creatures in combat (and, I assume, at other times as well). This seems to make them unable to hit the player. While you are on top of them you can walk around on them as if they were a surface.
(RM-1192 from redmine: created on 2014-03-09 by Tormod Hellen, , closed on 2014-12-17 by scrawl ., relates #1431 (closed))