How the Colossal Fighter + Armory Arm OTK works

1. Equip Armory Arm to an opponent's monster that has at least 1900 ATK (more if there are any Warrior types in the Graveyard). It needs to be big enough to beat Colossal Fighter in battle.
2. Attack Colossal Fighter into the monster equipped with Armory Arm.
3. In Substep 7 - End of the Damage Step, both Colossal Fighter and Armory Arm's effects activate, inflicting damage to your opponent equal to Colossal Fighter's ATK and reviving your deceased Colossal Fighter from the GY.
4. Repeat steps 2-4 until you win.