Contested Game Ball

Whenever you're dealt combat damage, the attacking player gains control of Contested Game Ball and untaps it.
{2}, {T}: Draw a card and put a point counter on Contested Game Ball. Then if it has five or more point counters on it, sacrifice it and create a Treasure token.

Referee Squad

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
Vigilance
When Referee Squad enters, tap target creature an opponent controls and put a stun counter on it. (If a permanent with a stun counter would become untapped, remove one from it instead.)

Armillary Sphere

{2}, {T}, Sacrifice Armillary Sphere: Search your library for up to two basic land cards, reveal them, put them into your hand, then shuffle.

Sphere of Duty

If a green source would deal damage to you, prevent 2 of that damage.

Play of the Game

Assist (Another player can pay up to {6} of this spell's cost.)
Exile all nonland permanents.

Sokrates, Athenian Teacher

Defender
Sokrates, Athenian Teacher has hexproof as long as it's untapped.
Sokratic Dialogue — {T}: Until end of turn, target creature gains "If this creature would deal combat damage to a player, prevent that damage. This creature's controller and that player each draw half that many cards, rounded down."

Mascot Exhibition

Create a 2/1 white and black Inkling creature token with flying, a 3/2 red and white Spirit creature token, and a 4/4 blue and red Elemental creature token.

Fellwar Stone

{T}: Add one mana of any color that a land an opponent controls could produce.

Interdisciplinary Mascot

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
Ward {3}
When Interdisciplinary Mascot enters, look at the top four cards of your library. Put one of them into your hand and the rest on the bottom of your library in a random order.

Strixhaven Stadium

{T}: Add {C}. Put a point counter on Strixhaven Stadium.
Whenever a creature deals combat damage to you, remove a point counter from Strixhaven Stadium.
Whenever a creature you control deals combat damage to an opponent, put a point counter on Strixhaven Stadium. Then if it has ten or more point counters on it, remove them all and that player loses the game.

Approach of the Second Sun

If this spell was cast from your hand and you've cast another spell named Approach of the Second Sun this game, you win the game. Otherwise, put Approach of the Second Sun into its owner's library seventh from the top and you gain 7 life.

Game Plan

Assist (Another player can pay up to {5} of this spell's cost.)
Each player shuffles their hand and graveyard into their library, then draws seven cards. Exile Game Plan.