/tg/-tan is simply described as a "pimp lich". He's essentially a skeleton in a wide coat with fur trimming and an eerily flaming tophat. He also occasionally carries a staff with a glowing giant d20 on top, and a rulebook that likely contains more rules than its modest size would suggest.
Apart from his presumable love for traditional games as mostly evidenced by his accessories, very little is known about /tg/-tan. Early artwork suggests he's the former half/tg/-tan now transformed into an undead with far greater self esteem, but this information is not verified.