  Dynamic Difficulty Adjustment (DDA) is a mechanism used in video games that
automatically tailors the individual gaming experience to match an appropriate
difficulty setting. This is generally achieved by removing pre-defined
difficulty tiers such as Easy, Medium and Hard; and instead concentrates on
balancing the gameplay to match the challenge to the individual's abilities.
The work presented in this paper examines the implementation of DDA in a custom
survival game developed by the author, namely Colwell's Castle Defence. The
premise of this arcade-style game is to defend a castle from hordes of oncoming
enemies. The AI system that we developed adjusts the enemy spawn rate based on
the current performance of the player. Specifically, we read the Player Health
and Gate Health at the end of each level and then assign the player with an
appropriate difficulty tier for the proceeding level. We tested the impact of
our technique on thirty human players and concluded, based on questionnaire
feedback, that enabling the technique led to more enjoyable gameplay.
