use whatever actions u want, such as a dummy spell as said before, and when its triggered
either
pick all units in 64.00 range of ((position of casting unit_\) offset by (96.00) towards (facing angle of casting unit))
if unit is not owned by owner of casting unit then set unit life to unit life - 20
set temp unit = random unit from (stuff above)
set temp unit life = temp unit life - 20
at least something like that would be the MOST basic way