There had been a lot of discussion on how an assassin can effectively deliver a Death Attack. It’s an extraordinary ability, not a feat, and oe like this:
Death Attack (Ex)
If an assassin studies his victim for 3 rounds and then makes a sneak attack with a melee weapon that successfully deals damage, the sneak attack has the additional effect of possibly either paralyzing or killing the target (assassin’s choice). Studying the victim is a standard action. The death attack fails if the target detects the assassin or recognizes the assassin as an enemy (although the attack might still be a sneak attack if the target is denied his Dexterity bonus to his Armor Class or is flanked). If the victim of such a death attack fails a Fortitude save (DC 10 + the assassin’s class level + the assassin’s Int modifier) against the kill effect, she dies. If the saving throw fails against the paralysis effect, the victim is rendered helpless and unable to act for 1d6 rounds plus 1 round per level of the assassin. If the victim’s saving throw succeeds, the attack is just a normal sneak attack. Once the assassin has completed the 3 rounds of study, he must make the death attack within the next 3 rounds.
If a death attack is attempted and fails (the victim makes her save) or if the assassin does not launch the attack within 3 rounds of completing the study, 3 new rounds of study are required before he can attempt another death attack.
I investigated the sneak attack rules and came to some conclusions.
To get to a point where you can use your assassin abilities, a series of distinct events have to take place. But the most important among them is arranging circumstances so that you can conduct a sneak attack. According to the rules,
The rogue’s attack deals extra damage anytime her target would be denied a Dexterity bonus to AC (whether the target actually has a Dexterity bonus or not), or when the rogue flanks her target.
Further, the Paizo messageboards describe those situations in greater detail:
Target is Flanked
Target is Surprised
Target is Flat Footed
Target is in a situation where it’s denied it’s dexterity bonus to AC (whether it actually has a bonus or not)
Target is Helpless
Target has been successfully feinted
Various magic items or feats or conditions that can recreate or include the above conditions.
Unless one of these conditions is met, you can’t do a sneak attack. If you can’t do a sneak attack, you can’t conduct your various assassin-based abilities. Taking each in turn:
Flanking: When making a melee attack, you get a +2 flanking bonus if your opponent is threatened by another enemy character or creature on its opposite border or opposite corner. Basically, if you and an ally are on diametrically opposite sides of a single opponent, that opponent is flanked and “sneak attack” is in effect.
Surprised: From stealth only (e.g., a stealth check) the first attack would be a sneak attack. If you have greater invisibility (and your opponent cannot detect invisible enemies) all attacks would be sneak attacks. Your Stealth check is opposed by the Perception check of anyone who might notice you. Creatures that fail to beat your Stealth check are not aware of you and treat you as if you had concealment. You can move up to half your normal speed and use Stealth at no penalty. When moving at a speed greater than half but less than your normal speed, you take a –5 penalty. It’s impossible to use Stealth while attacking, running, or charging.
Flat Footed: A character who has not yet acted during a combat is flat-footed, unable to react normally to the situation.
Helpless: A helpless opponent is someone who is bound, sleeping, paralyzed, unconscious, or otherwise at your mercy.
Feinted: Feinting is a standard action. To feint, make a Bluff skill check. The DC of this check is equal to 10 + your opponent’s base attack bonus + your opponent’s Wisdom modifier. If your opponent is trained in Sense Motive, the DC is instead equal to 10 + your opponent’s Sense Motive bonus, if higher. If successful, the next melee attack you make against the target does not allow him to use his Dexterity bonus to AC (if any). This attack must be made on or before your next turn
Operationally, there are several ways you can get to sneak attack:
Get in a flanking position; this would require (a) other players, and (b) good maneuverability (which is demonstrated by high speed [30+] and a way to moderate getting attack of oppertunity-ed to death (like by Mobility and Spring Attack feats)
Surprise people, by using stealth. if you can Stealth to within attack range without being detected by your intended victim, your first attack is a sneak attack.
Flat Footed: if you choose victims and attack them prior to them attacking or being attacked by anyone else, then that’s a sneak attack. I don’t how feasible this one is, because you’d almost certainly have to use stealth as well to get close enough, in a battle situations. The one time I think you would be able to do this would be in a non-combat situation, where you are in effect sneak attacking a victim that doesn’t see you as a combatant – a bartender at an inn you might be in, or something like that.
Helpless is obvious, and not overly helpful
Feinted is intriguing. it’s a two round effort BUT you can do it while in combat. However, Death Attack requires a couple things:
If an assassin studies his victim for 3 rounds
a sneak attack with a melee weapon that successfully deals damage
Studying the victim is a standard action.
The death attack fails if the target detects the assassin or recognizes the assassin as an enemy
Because Death Attack requires that the assassin not be detected until the moment he strikes, feinting can’t help you conduct a Death Attack. It will still get you a sneak attack, and all those sneak attack damage bonuses though.
Personally, I think that the best shot at delivering Death Attacks is to use Stealth: three rounds of Stealth checks vs. the victims Perception checks to get close, then you strike from Stealth, get the Sneak Attack, and kablammo.
Second best is flanking. Someone else is fighting someone, you come up behind after studying, and kablammo. The rest, I don’t think are feasible except in unusual situations.