Spell Burst

Buyback {3} (You may pay an additional {3} as you cast this spell. If you do, put this card into your hand as it resolves.)
Counter target spell with mana value X.

Steady Progress

Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)
Draw a card.

Talisman of Creativity

{T}: Add {C}.
{T}: Add {U} or {R}. Talisman of Creativity deals 1 damage to you.

Contentious Plan

Counterspell

Mana Geyser

Add {R} for each tapped land your opponents control.

Jeska's Will

Choose one. If you control a commander as you cast this spell, you may choose both instead.
• Add {R} for each card in target opponent's hand.
• Exile the top three cards of your library. You may play them this turn.

Disallow

Counter target spell, activated ability, or triggered ability. (Mana abilities can't be targeted.)

Mizzix of the Izmagnus

Whenever you cast an instant or sorcery spell with mana value greater than the number of experience counters you have, you get an experience counter.
Instant and sorcery spells you cast cost {1} less to cast for each experience counter you have.

Storm-Kiln Artist

Storm-Kiln Artist gets +1/+0 for each artifact you control.
Magecraft — Whenever you cast or copy an instant or sorcery spell, create a Treasure token.

Treasure Cruise

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)
Draw three cards.

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Boseiju, Who Shelters All

Boseiju, Who Shelters All enters tapped.
{T}, Pay 2 life: Add {C}. If that mana is spent on an instant or sorcery spell, that spell can't be countered.

Command Tower

Sol Ring

Izzet Signet

Mana Drain

Counter target spell. At the beginning of your next main phase, add an amount of {C} equal to that spell's mana value.

Command Beacon

{T}: Add {C}.
{T}, Sacrifice Command Beacon: Put your commander into your hand from the command zone.

Myriad Landscape

Myriad Landscape enters tapped.
{T}: Add {C}.
{2}, {T}, Sacrifice Myriad Landscape: Search your library for up to two basic land cards that share a land type, put them onto the battlefield tapped, then shuffle.