Sea Monster of Theseus #MAMO-EN071

Sea Monster of Theseus #MAMO-EN071 collector guide

About Sea Monster of Theseus

Sea Monster of Theseus is a Fusion Monster, made from its Fusion Materials with a card such as Polymerization, printed as MAMO-EN071 in Magnificent Monsters (2026) as an Ultra Rare. It is a Level 5 WATER Zombie monster with 2,200 ATK and 1,800 DEF. Magnificent Monsters is a 2026 set, and its highest rarities include some of the most valuable modern Yu-Gi-Oh! cards we track. Ungraded, this printing ranks 129th of the 220 Magnificent Monsters cards we track. The top card is Dark Magician, the Pharaoh's Servant at €40,161.

Character and collecting appeal

Zombies are built around the Graveyard, bringing monsters back again and again.

Version and identification

Check the code printed below the artwork on the right: it should read MAMO-EN071. MAMO-EN071 is the English printing. Other languages use their own letters in place of EN, such as DE or FR, and are priced separately. It is the Ultra Rare version. Ultra Rares have a gold-foil name and holographic artwork.

Price history

Today an ungraded copy of this printing sells for about €1.18, a PSA 9 for €5.35 and a PSA 10 for €29.12. Our monthly prices for it go back to August 2026. Its highest monthly ungraded value was €3.46 in August 2026, 66% above today.

Grading and population

A PSA 10 sells for 24.7× the ungraded price and 5.4× a PSA 9. That gap is small, so grading fees may outweigh the gain unless the card is for your own collection. Modern foils can leave the pack with scratches, print lines or a slight curl, so even fresh copies do not always reach a 10.

Investment potential

In its favour: a price well below its August 2026 peak, which some collectors see as room to recover; an active market (25 recent completed sales), so it is easy to sell. Against it: large modern print runs, which tend to cap prices unless a card becomes iconic. Card prices can fall as well as rise, so this is not financial advice.

Before you buy

Expect to pay around €1.18 for a clean ungraded copy; played copies sell for less, and a PSA 9 costs about €5.35. Ask the seller to show the code MAMO-EN071 and the Ultra Rare finish clearly in the photos, as listing titles often mix up printings. Modern foils can be scratched or curled straight from the pack, so check the surface under a light if you plan to grade.

Card details and image from YGOPRODeck. Yu-Gi-Oh! is a trademark of Konami; Search Cards is not affiliated with Konami.