doctorbadwolf
Heretic of The Seventh Circle
That’s certainly part of the concept, part of the core of the concept even. But the concept has grown bigger than that, and includes characters like Black Widow, Hawkeye, Winter Soldier, the AssCreed Assassins (Connor fights), and others who are quite capable in a fight. And it makes sense. What if the only way into the lord’s chamber is through a door that is never unguarded? Come outta nowhere and knock heads into the wall, while being strong enough to make sure the bodies fall slowly and quietly. Or, again, that scenario where the kill can only happen under guard, and you’re just gonna have to run a fighting escape.Assassin is a tricky concept to make a solid D&D class out of IMO because combat is such a significant part of the game, and an assassin isn’t really a combatant. If they’re doing their job right, there shouldn’t be a fight. If they’re really good, there shouldn’t even be a death. Just a knife in the pillow to show they could kill you if they want and a note with their demands. At least, that’s my view of assassins, as opposed to mere hit-people.
And that’s the thing, you aren’t a Fighter. You just know how to fight your way past some people to get to a target or get away.
Oh I agree. It doesn’t need an official release or anything. But hey, if we’re home brewing, is that really an important concern?Again I think that while @Fenris-77 and @Charlaquin raise good points, and while I personally don't think that the class needs to be added as a full class to 5e, I also think that there's a rich line of fictional "assassins" that people often want to model.
What that says about us as a society, eh, that's a different topic of conversation! But between videogames, film, and TV, I get the archetype and desire for it.

But yeah, from the AssCreed games to The Winter Soldier and other MCU assassins, to 007, I’d say it’s an archetype with some real legs. Nice legs. Good strong thicc legs. Happy Valentine’s Day Y’all.
For sure. That’s why I want to be able to apply a shroud when init is rolled, but also as a bonus action, and get something like Extra Attack. you’re competent in a normal fight, like say, The Winter Soldier, but you’re truly lethal when you have prepared the kill.If you want dangerous in round one the Rogue archetype is great at it. I'd suggest mechanics that support more than one play style, whatever that looks like, but generally pointed at solid DPR and some nova rather than insane nova potential.
since shrouds reduce crit range and add damage dice, striking from stealth (and thus with advantage) is really lethal.
Maybe they should be “the best at stealth in combat”? When you crit or drop a creature to 0, you can use any remaining movement, and Hide as part of the Attack Action used to make the attack?
Yes. min fact, I can see a subclass that uses its allies as weapons, applying shroud damage when an ally hits the target.I'd suggest that it isn't. SpecOPs clearing rooms in any video game is pretty dungeon crawly. Plus it's a lot more team oriented than the Rogue Assassin, which is, I think, key to what the OP is looking for,
Got a couple non-starters in there, for me, but there are some good ideas too. 1/encounter is a hard no, as is any alignment restrictions of any kind.What does (or should) an Assassin-class character do better than anyone else? What should its niches be? What should its weaknesses be? Let's start from there, basing it off Rogue.
What does (or should) an Assassin do better than anyone else, and what should its niches be?
Disguise. This should be a true niche of the class; have them be by far the best at physical disguises (which, note, things like True Sight will still be fooled by); other classes can try this at low-ish odds of success but Assassins can do it almost perfectly right out of the gate.
Poison. This should also be a class niche. Assassins are trained to recognize poisons, apply and administer them, treat or cure them with antidotes, and - at later levels - develop their own. Other classes can try some of these but at low-ish odds; except apply and administer which anyone can do only the Assassins is at much less (or zero) risk of accidentally administering poison to him/herself.
Killing. Against the right sort of targets (I'd suggest humanoids only, with size range increasing as level advances) this should be a class niche: only Assassins can one-shot kill on a good strike. This would require some tweaking of how 5e handles damage; in the specific case of Assassins a melee sneak attack that rolls 5 or more over what's required to hit bypasses hit points completely and either a) kills the target on the spot if the target is equal or lower level/HD than the Assassin or b) puts the target at 0 h.p. and into death saves if above the Assassin's level/HD. On a roll to hit that succeeds by less than 5 normal sneak attack damage still applies. Best of all, when attacking an unaware opponent they'd strike as if a Fighter of their level for the first attack.
Higher-level Assassins can use two weapons when doing this, with either one capable of a one-shot kill.
Stealth. Shared niche with other Rogue-type classes, with abilities about on par with Rogue for things like hiding, stealth, etc.
What should its weaknesses be?
Frontal melee. They're just not very good at it. They're unable to use anything other than light armour and their combat training (other than for killing strikes) is only slightly better than a Wizard.
Alignment. They have to be evil, because - and this is a 1e definition that I quite like - poison use is an inherently evil act.
Killing. Yes, this is also a weakness: the Assassin only gets to attempt the killing strike attack once per encounter; and if it misses the opponent(s) become(s) aware of the Assassin and the Assassin's in trouble. Note this differs from Rogue sneak attacks which they can keep using; an Assassin only gets one good shot.
That's enough to start with...![]()
And the combat weakness, tbh, at least how you describe it. Watch some videos on how combat works in the first 3 Assassins Creed games. The assassin can tangle, they have to be able to sometimes, because sometimes the only way to get to a target is to bypass guards that you will then have to fight to escape the scene. So, things like Bonus action Dodge, Reaction counterattack on a miss.
Disengage (no action) when you drop a creature to 0hp. Etc. Combat mobility and slipperiness, differently than the rogue does it.
But, yes to light armor, no weapons bigger than a short sword (for most subclasses), d8 hit dice.
Evasion, but Bonus Action Dodge instead of Uncanny Dodge.
Maybe instead of a normal Extra Attack, or as a level 11 thing, or something, you can move and make an attack as part of the same action when you drop a creature to 0hp. Get that Assassins Creed thing where you leap from the guy you just ganked to gank another dude, in one quick burst of lethal movement.
As for poison and disguise, they should be proficiencies, but not a big focus of the base class.