Sojourner's Companion

Affinity for artifacts
Artifact landcycling {2} ({2}, Discard this card: Search your library for an artifact land card, reveal it, put it into your hand, then shuffle.)

Pithing Needle

As Pithing Needle enters the battlefield, choose a card name.
Activated abilities of sources with the chosen name can't be activated unless they're mana abilities.

Welding Jar

Sacrifice Welding Jar: Regenerate target artifact.

Signal Pest

Battle cry (Whenever this creature attacks, each other attacking creature gets +1/+0 until end of turn.)
Signal Pest can't be blocked except by creatures with flying or reach.

Darksteel Citadel

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.)

Ornithopter

Thought Monitor

Affinity for artifacts
Flying
When Thought Monitor enters the battlefield, draw two cards.

Frogmite

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

Vault of Whispers

Aether Spellbomb

{U}, Sacrifice Aether Spellbomb: Return target creature to its owner's hand.
{1}, Sacrifice Aether Spellbomb: Draw a card.

Thoughtcast

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

Mistvault Bridge

Mistvault Bridge enters the battlefield tapped.
Indestructible
{T}: Add {U} or {B}.

Tinker

As an additional cost to cast this spell, sacrifice an artifact.
Search your library for an artifact card, put that card onto the battlefield, then shuffle.

Springleaf Drum

{T}, Tap an untapped creature you control: Add one mana of any color.

Memnite

Etched Champion

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

Sol Ring

Island

Cranial Plating

Equipped creature gets +1/+0 for each artifact you control.
{B}{B}: Attach Cranial Plating to target creature you control.
Equip {1}

Nihil Spellbomb

{T}, Sacrifice Nihil Spellbomb: Exile target player's graveyard.
When Nihil Spellbomb is put into a graveyard from the battlefield, you may pay {B}. If you do, draw a card.

Woodcaller Automaton

Prototype {2}{G}{G} — 3/3 (You may cast this spell with different mana cost, color, and size. It keeps its abilities and types.)
When Woodcaller Automaton enters the battlefield, if you cast it, untap target land you control. It becomes a Treefolk creature with haste and base power and toughness equal to Woodcaller Automaton's power and toughness. It's still a land.