New And Surprising Ways to Be Mean. Adversarial NPCs with Coupled
  Empowerment Minimisation
  Creating Non-Player Characters (NPCs) that can react robustly to unforeseen
player behaviour or novel game content is difficult and time-consuming. This
hinders the design of believable characters, and the inclusion of NPCs in games
that rely heavily on procedural content generation. We have previously
addressed this challenge by means of empowerment, a model of intrinsic
motivation, and demonstrated how a coupled empowerment maximisation (CEM)
policy can yield generic, companion-like behaviour. In this paper, we extend
the CEM framework with a minimisation policy to give rise to adversarial
behaviour. We conduct a qualitative, exploratory study in a dungeon-crawler
game, demonstrating that CEM can exploit the affordances of different content
facets in adaptive adversarial behaviour without modifications to the policy.
Changes to the level design, underlying mechanics and our character's actions
do not threaten our NPC's robustness, but yield new and surprising ways to be
mean.
