Someone casually mentioned this idea in passing, and I thought it was a such a brilliant and elegant idea I wanted a thread to expand on it.
The idea is this, if a creature is surprised, it is treated like a minion (ie one shot one kill). However, when the creature is not surprised, it has the full hit points of a regular monster.
This is a great way to do stealth adventures in dnd. A party can go on assassinating missions, knowing they can easily whatever they attack. But they have to be constantly weary, because once the surprise wears off, 30 minions becomes 30 regular guys.