I would also reduce health to around 30. Assassins are dps not tanks.

Also make poison a DOT ability.

Just reduce the sneak attack damage,  the poison damage, and maybe its stealth modifier. and it'll be a fun challenge for anyone at any level

I made my own assassin stat block because I didn't realize there already was one and it took like an hour because i'm bad at making monsters. : *(

I would argue that the poison effect should apply once on each sword (which would certainly lower the CR). Otherwise you either have to explain that for some reason your assassin ignores rules regarding the application of poison, or that these swords are magic and are available as loot, which for mid level parties, is quite busted as you've just given your party 2 shortswords that can deal a fireball's worth of damage in every attack.

Quote from ScarSent77 >>

I would argue that the poison effect should apply once on each sword (which would certainly lower the CR). Otherwise you either have to explain that for some reason your assassin ignores rules regarding the application of poison, or that these swords are magic and are available as loot, which for mid level parties, is quite busted as you've just given your party 2 shortswords that can deal a fireball's worth of damage in every attack.

 If the weapons are properly poisoned, the poison wouldn’t just go away after only 1 attack. You could however reduce the poison damage by 1d6 for every attack made, but removing the damage completely after one attack will just, as you said, make the assassin to weak. 

Yeah if he does both of his short sword attacks on a surprised creature he will do 20d6 + 6 + poison damage. Granted they make the poison con save twice and take each roll full or half depending on their roll. Which can add up to another 48 damage lol. 

The guy does over a 100 damage on average on a surprised target even if the poison damage isn't doubled lol. I don't think you need it.

This is broken. No abilities unattainable by the assassin class should not apply to a NPC assasin.

Odd comment, Grogg.  A PC assassin can absolutely do this (if he has access to the wyvern poison for the blades).  They are deadly AF on the first round.  And sometimes they die on the second round, because they are necessarily out front, doing this 100+ damage to an unsuspecting surprised target... and all his allies gank the assassin right afterward!

And PCs generally *can't* do a lot of things that monsters and NPCs can do.  An army's phalanx-trained soldiers can attack with reach weapons past their allies without the +2 cover mod, for example; minus homebrew feats, PCs can't.  Different training, different rules.  Maybe they come from an order that practices magical or alchemical modification of their initiates (ala Witcher)?

What’s the math behind the assassins stealth skill at +9 but the acrobatics is only +6? 

The Assassin has expertise in Stealth.

Crawford confirmed that the poison is determined by the saving throw, not the attack. And although Roll20 may not be a final rules arbiter, if you roll the assassin attack until you get a crit, it does not double the poison damage dice. 

https://bit.ly/3Glztq2

You don't take critical poison damage.

From the future, you are wrong! +6 SIR , thank you for posting this 4 years ago.

Quote from Suboshi >>

Yep, this is correct.  A crit here would be (1d6 x 2) + 3 for base dmg, then the ~24 (7d6) poison damage if failed saving throw after.

 Sneak Attack damage is doubled on a critical hit.  

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. 

The simplestway should be to take the "Master Thief" it is a CR 5 monster and a pretty scaled down Assasin.

Quote from Suboshi >>

Yep, this is correct.  A crit here would be (1d6 x 2) + 3 for base dmg, then the ~24 (7d6) poison damage if failed saving throw after.

 Sneak Attack damage is criticaled.  

I hate this monster profile.  Very poorly thought out.  The weapons, while obviously coated with Wyvern Poison, don't require the 1-round mechanic to enact, nor do they expire after 1 minute, and every player who kills an assassin expects to now have a 7d6 poisoned blade & crossbow bolts.  At least if you control the encounter as the DM you can off-screen poison for effect before the kill attempt and justify it as expiring, but when the assassins are spotted and confronted, and viola, they already have poisoned weapons and crossbow bolts with no prep and no duration, it's understandably infuriating for the player who only loots a standard short sword, light crossbow, and bolts.  I mean, you don't have a spellcaster using a Wand of Fireballs against the party and it's not there for loot, right?  You don't have an enemy in plate armor who doesn't have any to loot after the battle.

And sorry, I'm not giving out permanent +7d6 poison per hit weapons.  No way.  No how.

I generally make sure that these assassins always take the time to enact poisoning their weapons (or flee and poison if outed), carry at least 2 vials of Wyvern Poison each, and in addition to that, leave a clue for a stash nearby.  If the party is smart, it can be a really rewarding encounter.  If they're not, they're often paying for revival services.  

I was looking at this block and thinking the same thing.  The wyvern poison stats I saw said that it loses potency after the hit, so why do these weapons keep potency for each hit if they aren’t magical?  This addendum makes the most sense to me

This is untrue.