Battle Fusion

Quick-Play Spell

When an attack is declared involving a Fusion Monster you control and an opponent's monster: That monster you control gains ATK equal to the ATK of the opponent's monster, until the end of the Damage Step. You can only activate 1 "Battle Fusion" per turn.

Rulings – Yugipedia

Printings:

Dragons of Legend: DRLG-EN017 (Super Rare) - 2014-04-25
Fusion Enforcers: FUEN-EN056 (Super Rare) - 2017-02-23
Dragons of Legend: The Complete Series: DLCS-EN019 (Common) - 2020-09-10

Prices:

Cardmarket: 0.07 €
TCGplayer: $ 0.17