"Ryu Kokki" is based on the last boss of the Japan-only Famicom game released by Konami in 1987, Getsu Fūma Den. In the game, it transforms two times (it has three forms), and the card illustration depicts its final form. The protagonist, "Getsu Fuhma", also has a card with similar effect based off it.
"Ryu Kokki" makes an appeareance in Konami's Castlevania: Harmony of Despair under the name "Ryukotsuki" as a fightable boss in Chapter 11 DLC. All 3 forms are in 8-bit. The only difference is that his third form having more attacks than its previous version.