This is in response to Lands of Ara, again, too long to comment there.
Just last night our Assassin PC got to use his mojo. I read the rules again and things finally started clicking regarding Move Silently / Hide in Shadows / Invisibility and a victim’s vulnerability to Backstab / Assassination.
Under the Assassin class, it says you can Backstab as a Thief can, or you can choose to Assassinate in surprise situations.
Under the Thief class, it describes Backstab as simply an attack “from behind” which seems problematic.
In a game with high Movement and no area-control like 3E’s Attacks of Opportunity, what prevents the Thief from just circling behind his opponent and Backstabbing every time? In my game I always figured everyone could turn around even when it’s not their turn. This means you would need four attackers on one defender for one of those attackers to get a back attack. Alternately, the Thief could attack from the shadows or Invisibly and attack the opponent’s rear. This was how we did it in the past: you need to susprise your opponent from some concealment like Invisibility.
Our Monk PC stunned a bandit sergeant by punching him REALLY WELL and I ruled that the bandit was vulnerable to backstab / assassination because he was at +4 to be hit from the stun effect. The only place worse for him to be would be paralyzed/sleeping/helpless and that would allow an automatic slay. So the Monk facepunched the dude and he reeled backward onto the Assassin’s two-handed sword.
Similarly, the Assassin snuck up behind some dudes and Backstabbed two. How? He knew they were there, they didn’t know he was there because he was stealthy, and so when he leapt out they had to roll surprise (2 in 6 normally, but here it was 4 in 6 because of his stealth) and they rolled a 4. That gave him 4 segments to beat their bongoes while they were surprised.
It makes sense, and gives the Thief and Assassin more opportunity to use their special abilities.
So you need to surprise your opponent to get Backstab or Assassination. How do you surprise? By leaping up normally, in which case the opponent might be surprised 1 or 2 segments. Or by stealth, which means he’s surprised 1 to 4 segments (4 in 6 roll). What qualifies as stealth? That the opponent can’t sense you.
Some ways you can achieve this:
A: Elf or Halfling in non-metal armor, 90′ from anyone non-stealthy (guaranteed unless you have to open a door, then only normal 2 in 6 surprise)
B: Successful Move Silently from a direction the opponent is not looking (because you can’t Hide in Shadows on the move).
C: Successful Move Silently while using Invisibility.
D: Boots & Cloak of Elvenkind, or similar (remember, the boots prevent sound of footfall, so you can’t wear armor other than leather)
So you see, it’s not about whether you attacked from concealment! Even if you attack with stealth you might not get a Backstab attempt! Note just how powerful the Elf / Halfling ability is. It amounts to 100% chance for Move Silently and Hide in Shadows. If the players can organize a whole party of strictly Elves and Halflings, in light or no armor, it could be super effective!
Also remember, lest you get too excited about how powerful stealth is, that you can lose a chance at surprise various ways. You might have someone too noisy in your party (anything heavier than Chainmail). A fight might have happened too near the enemy for them to be caught off-guard. A failed door-bashing attempt means anyone inside the room can’t be surprised. Some monsters are less likely to be surprised, or immune. Others have special senses that tell them the PCs are coming (vibrations in the ground, life-detection). A monster might be hidden and on watch and the PCs wander by, not engaging the monster until a whole round passes and any potential Surprise on his part would be a moot point.
Finally, Assassination and Backstab aren’t Weapons Without Answer. They won’t pierce Stoneskin, or a Magic Weapon Required monster (unless you have enough magic on your weapon). Against a Fire Shield type defense, I’d say an Assassination effectively caused the creature’s remaining HP plus 10 (to bring it to -10 HP). High AC is a good defense, as are Mirror Images and other such distractions. In the case of the bandits, it was unclear at first who the leader-types were, which might make an Assassination pointless since it slays a random goober instead of someone important. Assassination is a percentage based on the victim’s Level/HD and the Assassin’s Level. The chart makes it quite hard to slay anyone higher than you and not much easier than 50% for people lower than you.
Side note: the Assassin and the Monk teamed up Lankhmar style and went looking for a law-breaker to beat up in the slums before the rest of the players arrived. I was tickled.