Guardian Baou

Level 4 DARK/Fiend Effect Monster
800 ATK / 400 DEF

Cannot be Summoned unless you control a face-up "Wicked-Breaking Flamberge - Baou". When this card destroys an opponent's monster by battle and sends it to the Graveyard: It gains 1000 ATK. Negate the effects of monsters destroyed by battle with this card.

Rulings – Yugipedia

Printings:

Dark Crisis: DCR-008 (Rare) - 2003-12-01
Dark Crisis: DCR-EN008 (Rare) - 2003-12-01
Dark Revelation Volume 1: DR1-EN170 (Common) - 2005-03-19
Legendary Collection 3: Yugi's World Mega Pack: LCYW-EN132 (Common) - 2012-09-29

Prices:

Cardmarket: 0.02 €
TCGplayer: $ 0.17