The sword's power changes with time, and as it racks up more kills. Soon, it gains a +1 to attack and damage. Then, it can become wreathed in flame as a bonus action. Then, it grants advantage to checks made to locate creatures. Then, its base power inverts and it can only kill non-evil creatures.
Do not tell the player about that last one. Insist to the player that it works exactly as you first described. The Paladin can kill innocent shopkeepers and little old ladies, but cannot kill this assassin working for the BBEG.
Will he question his own stab-first ask-later methods? Or will he turn evil without even noticing?
If I were doing this, I wouldn't describe the effects exactly (except the +1). I would just tell them it misses every time they attack a non-evil character first, and describe it being wreathed in flames. Then for the swap just tell them who it misses or hits still, but they have to figure out both times what the effect is (or that it changed).
Have him stab the mayor who's evil because he's greedy and selfish and borderline abusive in trade-deals with neighboring regions but is otherwise beloved (and has rewards heaped on him) because he's so good at actually keeping order in the town and keeping their goodwill (although probably at least a little bit through some passive-aggressive blackmail). That's always fun.
I mean, that sounds very much like a paladin in unapologetic violation of one or more of their oaths.
don't paladins have an at-will detect evil?
or did they take that out in 5e?They do but it's 1+charisma mod per day uses. The 5e players I know would immediately start stabbing people just to save on resources.
did they change what at-will means in 5e?
cos in 3.5 it means no usage limit, just takes a standard actionlike so
ShowIt simply says they can use the feature that often. It never says that it's an at-will action/feature. "At-will" isn't even a game term in 5e as far as I'm aware.
fair enough, i've only played 5e a couple of times and never as a paladin or gm
Mine just stood stock still staring at people for 24 seconds before starting a conversation, detecting good/evil/law/chaos. Made for some very fun roleplay.