Omega HubOmega HubOmega HubKnightmare Mermaid on every Yu-Gi-Oh! TCG Forbidden & Limited List: its status today, when it was banned and each change across all 83 lists.
Yes. Knightmare Mermaid is Forbidden on the current TCG list (October 2026): no copies are allowed in a deck.
Knightmare Mermaid first went Forbidden on the October 2019 list, from Oct 14, 2019.
Knightmare Mermaid is on the list right now: Forbidden on the current October 2026 list.
TCG (Advanced Format) data from Yugipedia's Historic Forbidden/Limited Chart and each list's page. OCG lists are not included. Card names as printed in the TCG. Source: Yugipedia · Historic Forbidden/Limited Chart