Emerald Medallion

Green spells you cast cost {1} less to cast.

Spell Pierce

Counter target noncreature spell unless its controller pays {2}.

Ruby Medallion

Red spells you cast cost {1} less to cast.

Mystic Remora

Cumulative upkeep {1} (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
Whenever an opponent casts a noncreature spell, you may draw a card unless that player pays {4}.

Animist's Might

This spell costs {2} less to cast if it targets a legendary creature you control.
Target creature you control deals damage equal to twice its power to target creature or planeswalker you don't control.

Demonic Tutor

Search your library for a card, put that card into your hand, then shuffle.

Slip Out the Back

Put a +1/+1 counter on target creature. It phases out. (Treat it and anything attached to it as though they don't exist until its controller's next turn.)

Krosan Drover

Creature spells you cast with mana value 6 or greater cost {2} less to cast.

Cemetery Prowler

Vigilance
Whenever this creature enters or attacks, exile a card from a graveyard.
Spells you cast cost {1} less to cast for each card type they share with cards exiled with this creature.

Spellbinding Soprano

Whenever this creature attacks, instant and sorcery spells you cast this turn cost {1} less to cast.
Encore {3}{R} ({3}{R}, Exile this card from your graveyard: For each opponent, create a token copy that attacks that opponent this turn if able. They gain haste. Sacrifice them at the beginning of the next end step. Activate only as a sorcery.)

Cloud Key

As this artifact enters, choose artifact, creature, enchantment, instant, or sorcery.
Spells you cast of the chosen type cost {1} less to cast.

Myth Unbound

Your commander costs {1} less to cast for each time it's been cast from the command zone this game.
Whenever your commander is put into the command zone from anywhere, draw a card.

Feign Death

Until end of turn, target creature gains "When this creature dies, return it to the battlefield tapped under its owner's control with a +1/+1 counter on it."

Starnheim Aspirant

Angel spells you cast cost {2} less to cast.

Mizzium Skin

Target creature you control gets +0/+1 and gains hexproof until end of turn.
Overload {1}{U} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")