Urza's Incubator [Modern Horizons 3]

Urza's Incubator [Modern Horizons 3]Set: Modern Horizons 3 Type: Artifact Rarity: Rare Cost: {3} As Urza's Incubator enters the battlefield, choose a creature type. Creature spells of the chosen type cost 2 less to cast. "Our recruitment efforts are bringing in fewer fresh troops every day. We need a new strategy."Urza, to Tawnos

and sometimes

Spend this mana only to cast artifact spells

Shatterskull Pass is a pretty distant second

Set: Secret Lair Drop Series Type: Creature — Human Rogue Ally Rarity: Rare Cost: {1}{B} Whenever Zulaport Cutthroat or another creature you control dies

The Eldrazi hunger without limit and consume without pause

Set: Judge Gift Cards 2023 Type: Artifact — Equipment Rarity: Mythic Cost: {3} Equipped creature gets +2/+2 and has protection from red and from white

Set: Outlaws of Thunder Junction: The Big Score Type: Legendary Creature — Beast Noble Rarity: Mythic Cost: {G}{U}{R} Ward {1}

damage to you

Set: Summer Magic / Edgar Type: Creature — Wolf Rarity: Rare Cost: {G} Banding (Any creatures with banding

All four can be used as the key card when building a deck

Riptide survivor

choose a letter