If you would guess a card, instead just choose the outcome you want.
At the beginning of each opponent's upkeep, look at the top card of their library. Tell them the name of that card. They tell you its mana cost, type line, power, and toughness. Then reveal that card. If they got anything wrong, draw a card.

Extort (Whenever you cast a spell, you may pay . If you do, each opponent loses 1 life and you gain that much life.)
Whenever you tap a Swamp for mana, add an additional .

: This artifact becomes a 3/6 Golem artifact creature until end of combat. Activate only during combat.

Instant and sorcery spells you cast cost less to cast.
Whenever you cast an instant or sorcery spell, put a charge counter on this artifact. Then if there are four or more charge counters on it, you may remove those counters and transform it.

Reach
Whenever Six attacks, mill three cards. You may put a land card from among them into your hand.
During your turn, nonland permanent cards in your graveyard have retrace. (You may cast permanent cards from your graveyard by discarding a land card in addition to paying their other costs.)

Zombie spells you cast cost less to cast.
Zombie creatures you control get +2/+1.

: Exile target land card from a graveyard. Add one mana of any color. (Activate only as an instant.)
, : Exile target instant or sorcery card from a graveyard. Each opponent loses 2 life.
, : Exile target creature card from a graveyard. You gain 2 life.

Sekki enters with eight +1/+1 counters on it.
If damage would be dealt to Sekki, prevent that damage, remove that many +1/+1 counters from Sekki, and create that many 1/1 colorless Spirit creature tokens.
Sacrifice eight Spirits: Return this card from your graveyard to the battlefield.

Lifelink
Adelbert Steiner gets +1/+1 for each Equipment you control.

When Doctor Doom enters, create two 3/3 colorless Robot Villain artifact creature tokens named Doombot.
As long as you control an artifact creature or a Plan, Doctor Doom has indestructible.
At the beginning of your end step, you draw a card and lose 1 life.

You may have this creature enter as a copy of any creature on the battlefield, except it isn't legendary, is an artifact in addition to its other types, and has myriad. (Whenever it attacks, for each opponent other than defending player, you may create a token copy that's tapped and attacking that player or a planeswalker they control. Exile the tokens at end of combat.)

Flying
At the beginning of your upkeep, sacrifice this creature unless you pay .

Red spells you cast cost less to cast.

Each instant and sorcery card in your graveyard gains flashback until end of turn. The flashback cost is equal to its mana cost.
Flashback (You may cast this card from your graveyard for its flashback cost. Then exile it.)

If you would copy a spell one or more times, instead copy it that many times plus an additional time. You may choose new targets for the additional copy.
, : Copy target instant or sorcery spell you control. You may choose new targets for the copy.

Your opponents can't cast spells from anywhere other than their hands.

Target player mills three cards.
Storm (When you cast this spell, copy it for each spell cast before it this turn. You may choose new targets for the copies.)

Haste
Whenever a creature an opponent controls dies, put a +1/+1 counter on Yahenni.
Sacrifice another creature: Yahenni gains indestructible until end of turn.

Whenever an opponent draws a card, this enchantment deals 1 damage to that player.

, Pay 1 life, Sacrifice this land: Search your library for a Plains or Island card, put it onto the battlefield, then shuffle.