Even though they are part of the OCG, Korean and Asian-English cards follow the TCG layout and artworks. Traditional Chinese cards follow the same layout and artworks as the Japanese ones. TCG cards are not legal in OCG tournaments. Due to Japanese, Asian-English and Korean cards having different backings, if a player chooses to use a mixture, they must use protective sleeves that cover the back of the cards. OCG tournaments are divided into three classes: Expert, which has no age restriction, Regular: for high school students and Challenge, for secondary school students.