Nightmare

Whenever this creature attacks or blocks, each opponent exiles the top two cards of their library.

Wilds of Eldraine Tokens

At the beginning of combat on your turn, if a card was put into exile this turn, put a +1/+1 counter on this creature.

The Nightmare arises from its lair in the swamps. As the poisoned land spreads, so does the Nightmare's rage and terrifying strength.

30th Anniversary Edition

Flying (This creature can't be blocked except by creatures with flying or reach.)
Nightmare's power and toughness are each equal to the number of Swamps you control.

The thunder of its hooves beats dreams into despair.

The List

Arena Beginner Set

Flying
Nightmare's power and toughness are each equal to the number of Swamps you control.

Ashiok, Nightmare Muse

+1: Create a 2/3 blue and black Nightmare creature token with "Whenever this creature attacks or blocks, each opponent exiles the top two cards of their library."
−3: Return target nonland permanent to its owner's hand, then that player exiles a card from their hand.
−7: You may cast up to three face-up cards your opponents own from exile without paying their mana costs.

[+1]: Create a 2/3 blue and black Nightmare creature token with "Whenever this token attacks or blocks, each opponent exiles the top two cards of their library."
[−3]: Return target nonland permanent to its owner's hand, then that player exiles a card from their hand.
[−7]: You may cast up to three spells from among face-up cards your opponents own from exile without paying their mana costs.