Helldritch
Hero
Wow... I would not like to have my party encounter such an assassin with the power to kill any number of persons so easily.
The assassination thing is already powerful. Ad_Hoc said that both criteria are relatively hard to come by... Not really. Do not forget that assassins are rogue. This means a high dexterity thus a good chance winning the initiative. This means a critical sneak attack a lot of times. There is a small chance for failure but failed assassinations are thing of both litterature and real life. And that is fine by me. The one assassin I have in my group often kill his target on the first or second round (as a party member will come to his aid and thus granting the second normal sneak attack). That is a lot of damage as there is no saving throw to reduce the damage of a sneak attack especially in an assassination attempt.
As for the scenario where the assassin is on improved invisibility...
Your other targets are pretty much aware that the assassin is somewhere around. The assassin will have advantage on attack rolls and thus make a sneak attack every single attack. If he position himself correctly, he could even get an OA and a second sneak attack with his reaction if a target moves away from him while searching for him. He might reveal his location that way but a sneak attack is a sneak attack and temptation can be high... That is a lot of potential damage. At only 4d6 of sneak attack it might represent 8d6 + 4d6 + 4d6 + 3 x weapon's damage + 3x the stat bonuses (the assassin would use his bonus action to hide). All this without saving throw. Add poison on top of that and not many characters of the same level can withstand that amount of damage. Do not forget that a critical on the follow up attacks is a real possibility as the assassin will attack with advantage. Critical on advantage is possible at around 7.5% of the time (I'm not entirely sure of the actual number but it seems about right, I should do the math but too lazy for it).
The assassin of my group is quite strong and he often kills on the first turn of whatever guards I have. He's not at 5d6 on a sneak so this means about 15d6 of additional damage as he is not alone when sneaking around (a monk is his partner).
The assassination thing is already powerful. Ad_Hoc said that both criteria are relatively hard to come by... Not really. Do not forget that assassins are rogue. This means a high dexterity thus a good chance winning the initiative. This means a critical sneak attack a lot of times. There is a small chance for failure but failed assassinations are thing of both litterature and real life. And that is fine by me. The one assassin I have in my group often kill his target on the first or second round (as a party member will come to his aid and thus granting the second normal sneak attack). That is a lot of damage as there is no saving throw to reduce the damage of a sneak attack especially in an assassination attempt.
As for the scenario where the assassin is on improved invisibility...
Your other targets are pretty much aware that the assassin is somewhere around. The assassin will have advantage on attack rolls and thus make a sneak attack every single attack. If he position himself correctly, he could even get an OA and a second sneak attack with his reaction if a target moves away from him while searching for him. He might reveal his location that way but a sneak attack is a sneak attack and temptation can be high... That is a lot of potential damage. At only 4d6 of sneak attack it might represent 8d6 + 4d6 + 4d6 + 3 x weapon's damage + 3x the stat bonuses (the assassin would use his bonus action to hide). All this without saving throw. Add poison on top of that and not many characters of the same level can withstand that amount of damage. Do not forget that a critical on the follow up attacks is a real possibility as the assassin will attack with advantage. Critical on advantage is possible at around 7.5% of the time (I'm not entirely sure of the actual number but it seems about right, I should do the math but too lazy for it).
The assassin of my group is quite strong and he often kills on the first turn of whatever guards I have. He's not at 5d6 on a sneak so this means about 15d6 of additional damage as he is not alone when sneaking around (a monk is his partner).