Frogmite

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)

Darksteel Citadel

Atog

Sacrifice an artifact: Atog gets +2/+2 until end of turn.

Rusted Relic

Metalcraft — Rusted Relic is a 5/5 Golem artifact creature as long as you control three or more artifacts.

Swamp

Tormod's Crypt

{T}, Sacrifice Tormod's Crypt: Exile target player's graveyard.

Tooth of Chiss-Goria

Flash
Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)
{T}: Target creature gets +1/+0 until end of turn.

Blade-Tribe Berserkers

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

Mountain

Glaze Fiend

Flying
Whenever another artifact you control enters, Glaze Fiend gets +2/+2 until end of turn.

Fleshgrafter

Discard an artifact card: Fleshgrafter gets +2/+2 until end of turn.

Galvanic Blast

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