Monk of the Long Death has the following abilities:
3rd level, Touch of Death: when you reduce a creature within 5 feet of you to 0 HP, gain temp HP = monk level + Wisdom bonus. (Combines in amusing ways with a Fast Hands Healer Thief BTW.)
6th level, Hour of Reaping: as an action, every creature within 30' that can see you must Wisdom save or be frightened until the end of your next turn. (Compare this to Berserker's 10th level Intimidating Presence, which works only on one creature within 30', and once a creature saves they are immune for 24 hours. Hour of Reaping comes sooner and is about five times as good.)
11th level, Mastery of Death: whenever you're reduced to 0 HP, can expend 1 ki point (no action/reaction required) to have 1 HP instead. (Makes you more unkillable than a barbearian, especially with temp HP and eventual Diamond Soul and Empty Body.)
17th level, Touch of the Long Death: as an action, expend between 1 and 10 ki points to touch a creature within 5 feet of you. Creature takes (2d10 x ki expended) points of necrotic damage, Con save for half.
The way I see this playing out in practice is that the monk (possibly with Alert feat) will do Hour of Reaping at the start of any nontrivial combat to protect his party and will move to place himself so that the enemy can't approach the party. If too many enemies made their saves, he may possibly add in Patient Defense to protect himself. If enemies try to bypass him to attack the party, put Stunning Strike on his opportunity attacks. Party will kill enemies to death with ranged attacks, then once the enemy morale shatters and they flee, monk will chase down an enemy and finish him off to gain temp HP. Rinse and repeat all day. It's pretty much the ultimate party tank.