As of now you cant have random values in an action. So e.g. summoning mobs around the player isnt really possible (only at the player or specific coordinates). Would be nice if that would be added.
Maybe something like this:

SUMMON minecraft:creeper ~${min:-3,max:3} ~ ~${min:-3,max:3}

another suggestion: for the REFLECT action to add the possiblity of selecting random players

Functions for "ExpressionEvaluator"