We give rogues advantage on the first round of combat if they attack someone who has not gone yet. Not sure where that came from. Seems like a thing carried over.
We have had rules creep in from computer games. Back when I regularly played 3.X one "rule" we had was that summoned monsters took XP from the party. I think this came from Everquest where a pet could take XP from the player if it did most of the damage.
