Opportunist Weapon

Weapon (any finesse weapon), rare (requires attunement by a rogue)

When you have advantage on the attack roll, attacks with this magic weapon score a critical hit on a roll of 19 or 20. You also gain this increased chance of a critical hit if another enemy of the target is within 5 feet of it, that enemy isn’t incapacitated, and you don’t have disadvantage on the attack roll.