Satan

Satan is, as you might expect, the main villain of the series. He's the former owner of Carbuncle and dotes on him frequently. He apparently has a liking to Hawaiian shirts. He is attracted to Arle Nadja and claims her to be his 'fiance' (though everyone else doesn't seem to think so) and wants to be with her under the starry night sky. According to some Compile profiles, he planned to give Carbuncle to his fiance, as proof of his love. As Carbuncle is with Arle, he is constantly chasing after her.

More often than not, he is the final character one must face in most Puyo Puyo titles. He is usually a powerful opponent too. With the notable exceptions of Puyo Puyo~n and Puyo Puyo 7, the Puyo in his stages are always programmed to fall at very high speeds, making him even more difficult to defeat.

(Source: Puyo Nexus)