Emergent Ultimatum

Search your library for up to three monocolored cards with different names and exile them. An opponent chooses one of those cards. Shuffle that card into your library. You may cast the other cards without paying their mana costs. Exile Emergent Ultimatum.

Maelstrom Archangel

Flying
Whenever this creature deals combat damage to a player, you may cast a spell from your hand without paying its mana cost.

Primeval Spawn

If this creature would enter and it wasn't cast or no mana was spent to cast it, exile it instead.
Vigilance, trample, lifelink
When this creature leaves the battlefield, exile the top ten cards of your library. You may cast any number of spells with total mana value 10 or less from among them without paying their mana costs.

Fertile Footsteps

Search your library for a basic land card, put it onto the battlefield, then shuffle. (Then exile this card. You may cast the creature later from exile.)

Have

Beanstalk Giant

Beanstalk Giant's power and toughness are each equal to the number of lands you control.

Beanstalk Giant // Fertile Footsteps

Ghalta, Primal Hunger

This spell costs {X} less to cast, where X is the total power of creatures you control.
Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)

Imoti, Celebrant of Bounty

Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom in a random order.)
Spells you cast with mana value 6 or greater have cascade.

Maelstrom Nexus

The first spell you cast each turn has cascade. (When you cast your first spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom in a random order.)

Fist of Suns

You may pay {W}{U}{B}{R}{G} rather than pay the mana cost for spells you cast.

Gandalf, Westward Voyager

Whenever you cast a spell with mana value 5 or greater, each opponent reveals the top card of their library. If any of those cards shares a card type with that spell, copy that spell, you may choose new targets for the copy, and each opponent draws a card. Otherwise, you draw a card. (A copy of a permanent spell becomes a token.)

Ruinous Ultimatum

Destroy all nonland permanents your opponents control.

Treasure Cruise

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

Jodah, Archmage Eternal

Flying
You may pay {W}{U}{B}{R}{G} rather than pay the mana cost for spells you cast.

Troyan, Gutsy Explorer

{T}: Add {G}{U}. Spend this mana only to cast spells with mana value 5 or greater or spells with {X} in their mana costs.
{U}, {T}: Draw a card, then discard a card.

Getting

Annoyed Altisaur

Reach, trample
Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom in a random order.)

Omniscience

You may cast spells from your hand without paying their mana costs.

Progenitus

Protection from everything
If Progenitus would be put into a graveyard from anywhere, reveal Progenitus and shuffle it into its owner's library instead.