Sea Monster of Theseus is a Fusion card in Yu-Gi-Oh Master Duel! Read on to see the card effect of Sea Monster of Theseus, its rarity, and all the packs used to unlock Sea Monster of Theseus! You can craft Sea Monster of Theseus using CP-SRs. To do so, go to the Deck Builder screen, search for Sea Monster of Theseus, then click on Generate.