Hard mode monsters

I know they move and attack faster, and they are higher level, but do they also do extra X% of damage?
cheers

The difference between levels of a character and a monster affect how much damage you do to them. Ie, you do more damage to level 18 monsters as a level 20 then against level 24 monsters. So yes, higher level monsters will hit harder, as well as having higher attributes, health, and armor level.