Armor Ninjitsu Art of Rust Mist

Continuous Trap

When a monster(s) is Special Summoned to your opponent's field, if you control a "Ninja" monster: Halve the current ATK of that Special Summoned monster(s).

Rulings – Yugipedia

Printings:

Order of Chaos: ORCS-EN069 (Super Rare) - 2012-01-20
Shadows in Valhalla: SHVA-EN030 (Super Rare) - 2018-08-16

Prices:

Cardmarket: 0.09 €
TCGplayer: $ 0.23