Mox Opal

Metalcraft — : Add one mana of any color. Activate this ability only if you control three or more artifacts.

Lumengrid Drake

Flying
Metalcraft — When Lumengrid Drake enters the battlefield, if you control three or more artifacts, return target creature to its owner’s hand.

Galvanic Blast

Galvanic Blast deals 2 damage to any target.
Metalcraft — Galvanic Blast deals 4 damage instead if you control three or more artifacts.

Etched Champion

Metalcraft — Etched Champion has protection from all colors as long as you control three or more artifacts.

Blade-Tribe Berserkers

Metalcraft — When Blade-Tribe Berserkers enters the battlefield, if you control three or more artifacts, Blade-Tribe Berserkers gets +3/+3 and gains haste until end of turn.