Rhystic Cave

{T}: Choose a color. Add one mana of that color unless any player pays {1}. Activate only as an instant.

Counterspell

Sisay, Weatherlight Captain

Sisay, Weatherlight Captain gets +1/+1 for each color among other legendary permanents you control.
{W}{U}{B}{R}{G}: Search your library for a legendary permanent card with mana value less than Sisay's power, put that card onto the battlefield, then shuffle.

Aether Membrane

Defender; reach (This creature can block creatures with flying.)
Whenever Aether Membrane blocks a creature, return that creature to its owner's hand at end of combat.

Psychotic Episode

Target player reveals their hand and the top card of their library. You choose a card revealed this way. That player puts the chosen card on the bottom of their library.
Madness {1}{B} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

Blood Moon

Wastes

Child of Alara

Trample
When Child of Alara dies, destroy all nonland permanents. They can't be regenerated.

Armageddon

Swirl the Mists

As Swirl the Mists enters, choose a color word.
All instances of color words in the text of spells and permanents are changed to the chosen color word.

Stasis

Players skip their untap steps.
At the beginning of your upkeep, sacrifice Stasis unless you pay {U}.

Etrata, the Silencer

Etrata, the Silencer can't be blocked.
Whenever Etrata deals combat damage to a player, exile target creature that player controls and put a hit counter on that card. That player loses the game if they own three or more exiled cards with hit counters on them. Etrata's owner shuffles Etrata into their library.

Misinformation

Put up to three target cards from an opponent's graveyard on top of their library in any order.

Prying Questions

Target opponent loses 3 life and puts a card from their hand on top of their library.

Void Winnower

Your opponents can't cast spells with even mana values. (Zero is even.)
Your opponents can't block with creatures with even mana values.

Mindslaver

{4}, {T}, Sacrifice Mindslaver: You control target player during that player's next turn. (You see all cards that player could see and make all decisions for the player.)

Smothering Tithe

Whenever an opponent draws a card, that player may pay {2}. If the player doesn't, you create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Forced Fruition

Whenever an opponent casts a spell, that player draws seven cards.

Spectacular Showdown

Put a double strike counter on target creature, then goad each creature that had a double strike counter put on it this way. (Until your next turn, those creatures attack each combat if able and attack a player other than you if able.)
Overload {4}{R}{R}{R} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")

Jin-Gitaxias, Core Augur

Flash
At the beginning of your end step, draw seven cards.
Each opponent's maximum hand size is reduced by seven.

Rhystic Study

Whenever an opponent casts a spell, you may draw a card unless that player pays {1}.

Pramikon, Sky Rampart

Flying, defender
As Pramikon, Sky Rampart enters, choose left or right.
Each player may attack only the nearest opponent in the chosen direction and planeswalkers controlled by that opponent.

True-Name Nemesis

As True-Name Nemesis enters, choose a player.
True-Name Nemesis has protection from the chosen player.