Rainbow Dark Dragon

Level 10 DARK/Dragon Effect Monster
4000 ATK / 0 DEF

(This card is always treated as an "Ultimate Crystal" card.)
Cannot be Normal Summoned/Set. Must be Special Summoned (from your hand) by banishing 7 DARK monsters with different names from your GY. You can banish all other DARK monsters from your field and GY; this card gains 500 ATK for each card banished this way.

Rulings – Yugipedia

Printings:

Phantom Darkness: PTDN-EN003 (Secret Rare) - 2008-02-13
Legendary Collection 2: The Duel Academy Years Mega Pack: LCGX-EN243 (Ultra Rare) - 2011-10-04
Ra Yellow Mega Pack: RYMP-EN099 (Common) - 2012-02-17
Battles of Legend: Relentless Revenge: BLRR-EN054 (Ultra Rare) - 2018-06-28
Legendary Duelists: Season 1: LDS1-EN100 (Common) - 2020-07-02
Structure Deck: Sacred Beasts: SDSA-EN010 (Common) - 2020-07-09
Speed Duel GX: Duel Academy Box: SGX1-ENI09 (Common) - 2022-03-17
Structure Deck: Legend of the Crystal Beasts: SDCB-EN008 (Common) - 2022-09-29

Prices:

Cardmarket: 0.08 €
TCGplayer: $ 0.09