Max Warrior

Level 4 WIND/Warrior Effect
1800 ATK / 800 DEF

If this card attacks an opponent's monster, this card gains 400 ATK during the Damage Step only. If this card destroys an opponent's monster by battle, until your next Standby Phase: this card becomes Level 2 and its original ATK and DEF are halved.

Rulings – Yugipedia

Printings:

Stardust Overdrive: SOVR-EN003 (Super Rare) - 2009-11-17
Duelist Pack: Yusei 2: DP09-EN009 (Rare) - 2010-01-15

Prices:

Cardmarket: 0.02 €
TCGplayer: $ 0.32