D&D Assassins: Best And Worst Mechanics

Is there a reluctance in D&D games to give Assassins the ability to kill? Consider this... 

• A 1st level Magic-User can slay at will with the spell Sleep -- which offers no saving throw and shuts down multiple foes of 4 hit dice or less. Considering that probably 90+% of all creatures in your fantasy world are 4 hit dice or less, your 1st level magic-user is stunningly powerful. Granted, they can only do this once/day until they gain more levels and/or scrolls.

Let's take a look at different versions of D&D to see how they handle an Assassin's ability to assassinate as well as other abilities like disguise and poison.

In no particular order or importance...

AD&D 1st Edition

•  A back-stab doing up to quintuple damage depending on your level. That option is for both assassins and thieves and serves as an argument against even having a separate assassin class. In most versions of D&D on this list, not counting 3.5, the back-stab (sneak attack) is merely double damage.)
• The assassination table (found in the DM's Guide, pg. 75) assumes you have delivered to your DM a detailed plan of your assassination attempt. Probably includes infiltration and disguise rolls. You have a base 50% chance of straight up killing your foe, depending on your level cross-referenced with theirs. If this fails, regular weapon damage is rolled, which might kill in and of itself, and also may require a save vs. poison if you are employing such tactics.
• As mentioned above, any option you choose can also employ the use of poison as a back-up, but the Player's Handbook discourages PCs using poison as it can be abused and there is mention of a check to see if you nick yourself, but it's unclear what that check is (just dawning on me now, is this a poison save? -- if so that's cool, but assassins should get some kind of bonus.)
• Also, the poison rules are overly concerned with people spotting the poison on your blade, not something I was ever concerned with.
• Disguise success is automatic with a increasing chance of being caught per day. 
• Assassins don't start getting thief skills until 3rd level.
• The Player's Handbook has a table displaying what you should be paid for your dirty deeds. This is cool. 
• Verdict: Not bad, but it's largely a flavor class. The 1st level thief is more capable.

D&D 3.5

• Dungeon Master's Guide, pg. 180 (I consider the 3.5 DM's Guide second only to the much beloved 1st Edition DM's Guide in it's overall usefulness.) Here, the Assassin is a Prestige Class requiring 4 ranks in disguise, and 8 ranks in both hide & move silently. 
• The best Assassin drawing I've ever seen in a D&D book (art by Wayne Reynolds.)
• Mechanics, the death attack -- here you have to make a sneak attack after studying your target for 3 rounds. If it hits, they must save vs. Fort DC:10 + your level + your Intelligence bonus or die instantly or (your choice) be paralyzed for 1d6 + your level rounds. If they make their save, you still do sneak attack damage. I love it all except for the 3 rounds of study. Nobody wants to voluntarily sit out the game for 3 rounds.
• This version of the Assassin can cast spells.
• Poison Use -- can use poison without poisoning themselves. Not really that exciting as anyone can use poison with only a 5% chance of poisoning themselves -- lame. And all variations of D&D lack good (or any) black market rules for locating things like poison. However, the Assassin does gain an increasing resistance to poison (bonus to save) as he levels up, so this is good as it displays tangible knowledge of the subject.
• Verdict: Good, except for the 3 rounds of study thing.

Pathfinder 1st Edition

• Very similar to the 3.5 Assassin. No spells though, but has variations on the death attack as you gain levels.
• Verdict: I prefer the 3.5 version.

D&D 5th Edition

• A sub-class of the Rogue starting at 3rd level.
• Assassinate -- You have advantage vs. someone who hasn't taken their turn and any attack is a critical hit if your foe is surprised. High level assassins can do a lot of sneak attack damage vs. surprised targets.
• Your 9th & 13th level abilities are lame as hell, campaign-based, infiltration and imposter abilities. Talk about empty levels.
• Death Strike at 17th level(!) surprised targets must save or take double the damage inflicted. Could be a massive amount of damage.
• Verdict: Disappointing. Yes, they can do a shit-ton of damage when they (finally) reach 17th level, but all of the mid-level abilities just focus on disguise type stuff, and poison isn't even mentioned. Everything is measured in damage. This is the Walt Disney Assassin. 

Labyrinth Lord (Advanced)

• Streamlines the percentage chance from AD&D 1st Edition. Here you don't have to turn in an elaborate plan to your DM, you simply attempt the (modified by levels) percentile roll after a successful back-stab.
• Disguise rules like in AD&D1st Edition.
• Can use poison of course, and again like 1st Edition.
• Verdict: Pretty good streamlined assassinations.

Swords & Wizardry

• No rules for assassination other than the suggestion to add damage equal to your level to any successful back-stab. This is because S&W is based on the Original Rules which apparently only had "off-screen" assassination mechanics for NPC assassins.
• Verdict: Disappointing. But, a few simple hacks...

Old School Essentials

• Assassination -- you must succeed on a back-stab attack, victim then saves vs. death with a penalty based on the assassin's level. Any human/demi-humans can be killed and monstrous humanoids up to 4 hit dice.
• Usual disguise stuff and victim's of the Assassin's poison (if they use it) suffer -2 to the save.
• Verdict: Very clean, one of the best. I would add -- a poison save bonus, treat disguise like a thief skill, a few spells. 

Castles & Crusades

• Death Attack is similar to the one from D&D 3.5 in that it requires 3 rounds of study, a sneak attack, and a save (constitution save.)
• Has an interesting ability called case target (wisdom check) which allows you to discern things like hit dice and hidden weapons or abilities, but it's all at the CK's (DM) discretion and it takes 1d3 x 10 minutes. This tilts toward being a flavor ability because it takes so much in-game time to do and depends a lot on discretion. I would change it to -- 1 secret discerned per round spent casing, so it can be beneficial right there in combat.
• Has the usual uninspiring disguise and poison stuff.
• Verdict: Okay. C&C classes have a lot of flavor abilities that I wish had more of an immediate mechanical impact. Still a nice game. Just tinker a bit.

Astonishing Swordsmen & Sorcerers of Hyperborea

• Assassination requires a successful back-stab as per the usual back-stab type rules, must be hidden, +4 "to-hit", etc. Then a second d20 is rolled according to a chart cross-referencing levels. If this second roll succeeds, the target then saves vs. death (no save is allowed if the "kill" roll was a 19 or 20).
• The usual poison and disguise stuff, except here disguise has a 1 in 6 chance and the disguise spell is referenced.
• Verdict: Okay, maybe one too many rolls. Should a death save be required after two rolls? Does sleep offer a save? -- No. Compromise -- Drop the second roll, keep the death save.

Basic Fantasy

• Assassinate -- Make a successful sneak-attack, victim saves vs. death. DM's discretion -- Victims 2 or more levels lower than you might be denied a save and no penalty for higher level victims -- wow!
• Can also waylay (knockout) someone using the Assassinate ability.
• No disguise mentioned, but they can make a dose of contact poison for 500 GP and this has a percentage chance of success like other thief abilities. Pretty cool, comes with a warning not to abuse this.
• Verdict: Not bad, pretty straight forward. Maybe the most generous one here.

HackMaster (5th Edition)

• Ok, for an old-school D&D clone, this game is crunchy. 1/3 of your hit points equals your Threshold of Pain (ToP). If you take more damage than your ToP, you need to roll under 1/2 your constitution or collapse, writhing in pain. 1st level Assassins deduct 1 from their target's ToP, and 1 more every two levels thereafter making it easier for them to drop you. If the damage is 5 or more higher than it needs to be, you're not only dropped, but dropped silently. 10 or more than it needs to be, and you fall flat out unconscious allowing for a Coup de Grace in just 2 seconds, where as other classes take 10 seconds. Got that?
• Poison is not mentioned and disguise is a skill anyone can take (I think.)
• Verdict: I think it works for this game as there are a lot of realistic aspects to this combat system. But damn, crunchy.

In summation and what would my perfect Assassin look like?

• My two favorites from the list above are from vastly different versions of D&D -- Old School Essentials and D&D 3.5 (I've always liked the 3.5 Assassin.) 
• I would like to see poison utilized more. Not just in using poison, but finding it in the black market or cultivating it from the wild. 
• Disguise should be treated just like a thief skill with instantaneous, on-the-spot results. Example -- the party slays some cultists or orcs or something roughly humanoid. The Assassin gathers up it's equipment and wanders into the next room containing more cultists/orcs, roll your disguise to see if it works. If it does, you gather some intel or pick some pockets. If it doesn't, it's much like failing a stealth check. When you distill it down, disguise is just stealth out in the open.
• Clean assassination rules. Successful sneak attack, then level-based save.
• Daggers are iconic assassination weapons and should be more integral to the class. Perhaps limit sneak attack (back-stab) to daggers only. This creates a decent risk. But in doing this, I would make them equal to, or close to, fighters in combat ability, while still limiting armor to leather.
• Magic use is optional for me, but makes sense. Assassins would definitely dabble in the dark arts to gain an edge.
• Visually, I like the mysterious, cloaked figure, dodging in and out of shadows, poisoned dagger in hand, striking to kill whenever he can.
• And here's a final thought -- you could link the death attack directly to poison. If they're out of poison, they can't make a death attack. This promotes the need to find and/or cultivate poison (which should be hard & expensive.) Start counting your doses. With this method, a back-stab isn't required (but you would still have that ability.) And perhaps a poison would only last so long on your blade, so once you apply it, time is of the essence.