Sad Ghouls is a singleplayer arcade survival shooter, where endless hordes of ghouls constantly stream into the arena.
Kill enemies to score points and increment the combo counter. Getting higher combo means better weapons and sometimes new weapons.
All score from kills gets multiplied by the combo counter. Choosing a higher difficulty setting results in tougher enemies that grant higher score. But a chill player can choose an easier difficulty to chill and still have a chance to appear on the leaderboard.