Mox Opal

Metalcraft — {T}: Add one mana of any color. Activate only if you control three or more artifacts.

Etched Champion

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

Chrome Steed

Metalcraft — Chrome Steed gets +2/+2 as long as you control three or more artifacts.

Vault Skirge

({B/P} can be paid with either {B} or 2 life.)
Flying
Lifelink (Damage dealt by this creature also causes you to gain that much life.)

Dispatch

Tap target creature.
Metalcraft — If you control three or more artifacts, exile that creature.

Snapsail Glider

Metalcraft — Snapsail Glider has flying as long as you control three or more artifacts.

Puresteel Paladin

Whenever an Equipment you control enters, you may draw a card.
Metalcraft — Equipment you control have equip {0} as long as you control three or more artifacts.