The Ursurper is a Neutral whose Goal is to end the game as King. As King, however, he acts more like an Neutral Killer than a normal Neutral, getting killing abilities.
Passive:
Bastard - As the King’s bastard, Royal Blood still flows within your veins. As such, you can step-up to become King during that phase.
Killing Intent - You’ll detect when you’re about to get killed and hide. This will make your attacker think they were occupied, but rend you unable to use your abilities during that night.
Day Ability:
Eavesdrop - During the day, you’ll be able to read all the Whispers to and from the King. (2 uses)
Night Abilities:
Disguise - Disguises your target, making them appear as the oposing faction to investigations during that same night.
Falsify - Choose a target and a role. If your target dies the next night or day, he will appear as the role you chose. (3 Uses)
As King
As a King, the usurper maintains the occupy-immunity and all the immunities of a normal King. However, he gets one aditional day ability, and two new night ones.
Day Ability
Poisoned Letter - You can Poison anyone who whispered you during this day. Max of 3 targets. (1 use)
Night Abilities
Enemies - Visit a player and check his role. If he’s not Neutral, you’ll execute him instead. (2 uses)
False Guard - Send a Guard to protect a player. The Guard will kill whoever visits that Player before they can do so. Can be self-targeted. (4 uses)
The idea behind the Ursurper is to use your Night abilities to trick the King into executing innocents, and to take his place when he’s put down. With Royal Blood and a good alibi, his chances are pretty good.
After that, comes the harder part - surviving. Unlike a normal King, the Ursurper has specific killing abilities to cut the game short. Like the Neutral King, his job is to win with one of the factions (or alone, if chaos ensues) and survive until the end of the game.