Bloodlines is a card game in which the players control noble houses attempting to accumulate titles while assassinating their rivals. It's heavily inspired by Keith Baker's Gloom, and was derived from some of the subsystems in an earlier game prototype.
Each round represents a generation. During the round, nobles accumulate lifepath cards (i.e., "Patronized the arts", "Entered the Church of the Moon", or "Appointed as Royal Cup-bearer") which give their nobles beneficial symbols such as Prestige and Intrigue.
Nobles may be either Strong, Ordinary, or Weak. The better the inherent quality of a noble, the more lifepaths they can accumulate.
At the beginning of each round, a random assortment of titles (i.e., "Grand Duchy of Fortalice", "Earldom of Rochefort") are drawn. A player's familiy must have a certain number of symbols of a certain type to acquire an available title.
To prevent each other from seizing available titles, players can assassinate rival nobles. Various iterations of the game accomplished this through "Assassin" cards, "Assassin" cards that doubled as "Bodyguard" cards (and countered each other), death lifepath cards ("Exiled for Fraud," "Poisoned at Table"), and murder lifepath cards ("Cheated at Duelling", "Ambushed a Rival").
Playtesters got genuinely angry at each other for assassinating each other's nobles - so angry, in fact, that they would often play suboptimally in order to exact revenge.
Rounds were extremely predictable until I introduced the mechanic of Season cards: a handful of cards, shuffled into the deck, that end the current round when they are all revealed. Players' inability to predict the end of the turn forced them to take calculated risks and created greater strategic depth.
The problem space in the average turn is too restricted. On about half of player turns, the most beneficial long-term move is completely obvious.
Assassination is clearly a mechanic that is core to the player experience. However, even after several iterations, I never found a rule that achieved all of the desirable properties of 1) costing the attacker an appropriate amount, 2) harming the defender an appropriate amount, 3) not introducing additional state logic into the game, and 4) being easy for players to remember.
Playtesting a synchronous, co-located game with more than two players is logistically difficult. Even after settling on a given ruleset and moving on to tweaking game variables, testing a given set of variables takes about 3-5 sessions.