In my 5E game, I sometimes use Minions (stolen from 4E). This allows me to add the ability to increase the drama without increasing the difficulty. Ultimately making a scene a bit more epic. The challenge is that when certain spells are used such as Sleep, there is not an easy action resolution.
The way I use Minions is: I give the Monster an AC of X and if the PC rolls X (or above) they kill the monster (regardless of what their damage dice result is). When I just use weak monsters from the 5E Monster Manual I have ran into situations where the PC's attack hits, but their hit dice roll is low and they take multiple turns to kill the monster, which just drags out combat unnecessarily.
What am I able to utilize in 5E that is Minion-like? Or perhaps how could I modify a 5E Monster that would satisfy the use of a spell like "Sleep"?