Rising thus: Shrek? (4)
I believe the answer is:
ogre
'shrek?' is the definition.
'rising thus' is the wordplay.
'rising' is a reversal indicator (going up in a down clue).
'thus' becomes 'ergo' (I've seen this before).
'ergo' written backwards gives 'OGRE'.
(Other definitions for ogre that I've seen before include "Monster, troll" , "Fairy-tale creature" , "Bugbear" , "Giant: monster" , "man-eater" .)