Unknown Synchron

Level 1 DARK/Machine Tuner Effect
0 ATK / 0 DEF

If your opponent controls a monster and you control no monsters, you can Special Summon this card (from your hand). You can only Special Summon "Unknown Synchron" once per Duel this way.

Rulings – Yugipedia

Printings:

Extreme Victory: EXVC-EN002 (Common) - 2011-05-06
Legendary Collection 5D's Mega Pack: LC5D-EN022 (Secret Rare) - 2014-10-23
Synchron Extreme Structure Deck: SDSE-EN008 (Common) - 2015-08-27
Legendary Duelists: Synchro Storm: LED8-EN049 (Common) - 2021-10-28

Prices:

Cardmarket: 0.05 €
TCGplayer: $ 0.08