Iry
Legend
Monsters can already do this. If the party is sound asleep and they keep failing their perception checks, an assassin could come in and take out the person on watch, then proceed from one party member to the next without anybody waking up. That is a LOT of failed perception checks, but it is possible.So in less than 30 feet my assassin has 5 combat encounters for the day. Your PC is surprise etc. Do think having this type of power would be fair and balanced.
Of course, this would be really miserable for the rest of the players and I wouldn't do it.