Two things :
I got spreading the love after using volley. I hit all five enemies. Therefore, grenades and firebombs aren't needed.
From this I can also assume that hots like buckshot, or any that display a cone, will work.
CAn anyone confirm quitting the mp matches unlocks the achievement?
352 completed games & apps to 100%
91.47% completion percentage
Last 100% Completion : Mortal Kombat X (1000g) (Xbox One)
Thanks to Rajeanero for the avatar and Mr Chaotix for the sig.