Sea of Clouds

Sea of Clouds enters tapped unless you have two or more opponents.
{T}: Add {W} or {U}.

Ancient Copper Dragon

Flying
Whenever Ancient Copper Dragon deals combat damage to a player, roll a d20. You create a number of Treasure tokens equal to the result.

Neera, Wild Mage

Whenever you cast a spell, you may put it on the bottom of its owner's library. If you do, reveal cards from the top of your library until you reveal a nonland card. You may cast that card without paying its mana cost. Then put all revealed cards not cast this way on the bottom of your library in a random order. This ability triggers only once each turn.

The Council of Four

Whenever a player draws their second card during their turn, you draw a card.
Whenever a player casts their second spell during their turn, you create a 2/2 white Knight creature token.

Tomb of Horrors Adventurer

When Tomb of Horrors Adventurer enters, you take the initiative.
Whenever you cast your second spell each turn, copy it. If you've completed a dungeon, copy that spell twice instead. You may choose new targets for the copies. (A copy of a permanent spell becomes a token.)

Mazzy, Truesword Paladin

Whenever an enchanted creature attacks one of your opponents, it gets +2/+0 and gains trample until end of turn.
Whenever an Aura you control is put into your graveyard from the battlefield, exile it. Until the end of your next turn, you may cast that card.

Robe of the Archmagi

Whenever equipped creature deals combat damage to a player, you draw that many cards.
Equip {4}
Equip Shaman, Warlock, or Wizard {1}

Morphic Pool

Morphic Pool enters tapped unless you have two or more opponents.
{T}: Add {U} or {B}.

Displacer Kitten

Avoidance — Whenever you cast a noncreature spell, exile up to one target nonland permanent you control, then return that card to the battlefield under its owner's control.

Archivist of Oghma

Flash
Whenever an opponent searches their library, you gain 1 life and draw a card.

Popular Entertainer

Commander creatures you own have "Whenever one or more creatures you control deal combat damage to a player, goad target creature that player controls." (Until your next turn, that creature attacks each combat if able and attacks a player other than you if able.)

Lae'zel's Acrobatics

Exile all nontoken creatures you control, then roll a d20.
1—9 | Return those cards to the battlefield under their owner's control at the beginning of the next end step.
10—20 | Return those cards to the battlefield under their owner's control, then exile them again. Return those cards to the battlefield under their owner's control at the beginning of the next end step.

Gond Gate

Gates you control enter untapped.
{T}: Add {C}.
{T}: Add one mana of any color that a Gate you control could produce.

Far Traveler

Commander creatures you own have "At the beginning of your end step, exile up to one target tapped creature you control, then return it to the battlefield under its owner's control."

Ancient Silver Dragon

Flying
Whenever Ancient Silver Dragon deals combat damage to a player, roll a d20. Draw cards equal to the result. You have no maximum hand size for the rest of the game.

Slaughter the Strong

Each player chooses any number of creatures they control with total power 4 or less, then sacrifices all other creatures they control.

Arcane Signet

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

Elminster

Whenever you scry, the next instant or sorcery spell you cast this turn costs {X} less to cast, where X is the number of cards looked at while scrying this way.
+2: Draw a card, then scry 2.
−3: Exile the top card of your library. Create a number of 1/1 blue Faerie Dragon creature tokens with flying equal to that card's mana value.
Elminster can be your commander.