Quote from StryderGate >>

It looks like there are some Assassin options missing from the Compendium here. I have MTOF on Roll20 and it has Assassin of Baphomet and Assassin of Levistus. I don't see those listed here in the Monster Compendium. What am I missing?

Perhaps they wasn’t considered different enough to have their own entries.

I’m afraid I don’t have the Tome of Foes, are those just assassins with cult of Levistus or Baphomemt traits?

powerful weapons!

Quote from DungeonDaddy >>

It's confirmed by Jeremy Crawford that poison does NOT apply to critical hits when poison is added to a weapon if there's a save involved, "Any damage dice delivered by a critical hit—as opposed to a saving throw—are rolled twice." 

 

Except that the damage dice for the poison are delivered by the critical hit (the attack), there's just an additional saving throw to allow you to take half damage from those die.  The poison damage die are still part of the attack, not part of a saving throw like they would be with the Fireball spell or something.

To each their own, but I still think the poison die should be doubled.  It is ultimately part of the attack.

Quote from DungeonDaddy >>

It's confirmed by Jeremy Crawford that poison does NOT apply to critical hits when poison is added to a weapon if there's a save involved, "Any damage dice delivered by a critical hit—as opposed to a saving throw—are rolled twice."  

 He's talking about  poison, basic (vial), which does NO damage if the target makes the saving throw. The assassin's poison damage (which is clearly wyvern poison (injury)) deals damage no matter what, so that amount is doubled and then the target can save for that damage to be halved.

So if an assassin surprises an adventurer and hits with two shortsword attacks (and the adventurer fails the DC 15 Constitution saving throw) then the Assassin does 120+ hit points of damage in one turn?  And the Assassin gets normal initiative for the next turn? That seems pretty OP. 

Quote from BenthicBiomancer >>

So if an assassin surprises an adventurer and hits with two shortsword attacks (and the adventurer fails the DC 15 Constitution saving throw) then the Assassin does 120+ hit points of damage in one turn?  And the Assassin gets normal initiative for the next turn? That seems pretty OP. 

 27*2

Quote from BenthicBiomancer >>

So if an assassin surprises an adventurer and hits with two shortsword attacks (and the adventurer fails the DC 15 Constitution saving throw) then the Assassin does 120+ hit points of damage in one turn?  And the Assassin gets normal initiative for the next turn? That seems pretty OP. 

 It’s more like 90+ points of damage, but yes that is indeed really terrifying.

I actually have to wonder how any kings survive with these guys around.

The average damage is 87 (if the poison doubles on a crit) or 62.5 (if it doesn't).

Quote from Thauraeln_The_Bold >>

The average damage is 87 (if the poison doubles on a crit) or 62.5 (if it doesn't).

 Precisely.  And, that’s just on its first hit.

Indeed, it's only on the first hit. The assassin must do this on the first round.

One killed my sister's level five character in one hit

instant Kill

It depends on the dm some people crit with everything others dont. I personally use the whole extra damage for both players and enemies since it beefs up things that get crits a lot more.

Would there be any way to make this a lower challenge rating? I want my party to fight one of these but I don’t want to make it a super hard challenge. 

Quote from JaysenCarter >>

Would there be any way to make this a lower challenge rating? I want my party to fight one of these but I don’t want to make it a super hard challenge. 

 You could easily adjust the stats.. just watched an older vid of Matt Colville ( Monkeying With Monsters, Running the Game ) in order to find inspiration. in my case to buff them up but he explains clearly enough both sides of the modifications. 
Remember, all the monsters/NPC's in the books are for inspiration. You are the DM of your world / adventure. Hope my advice helped :)

Quote from Dr_Frederick >>

Quote from BenthicBiomancer >>

So if an assassin surprises an adventurer and hits with two shortsword attacks (and the adventurer fails the DC 15 Constitution saving throw) then the Assassin does 120+ hit points of damage in one turn?  And the Assassin gets normal initiative for the next turn? That seems pretty OP. 

 It’s more like 90+ points of damage, but yes that is indeed really terrifying.

I actually have to wonder how any kings survive with these guys around.

Some combination of appeasement, very good security, and having a few of these guys of their own on retainer probably.

imagine one that only rolled ones

Very fun used it to bully a party of rouges as a DM

****

To lower the challenge rating, you have a few options:

- Remove the multi-attack (makes the assassin less likely to down your whole party but doesn't affect their ability to kill a single character)
- Take away their poison damage entirely (for a low-level party) or reduce the damage and/or saving throws (for an intermediate-level party)
- Reduce the sneak attack damage (probably in addition to reducing the poison damage, both of which reduce the potential for instant kills on critical hits)
- Play the assassin badly, or add environmental advantages for the characters (such as having the assassin only sneak attack characters who can tank the hit, or be caught unawares by the party instead of the other way around, or be in an area where they have limited time before the town watch descends upon them)