Prosperous Thief

Ninjutsu {1}{U} ({1}{U}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Whenever one or more Ninja or Rogue creatures you control deal combat damage to a player, create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

Ornithopter

Mesmerizing Benthid

When this creature enters, create two 0/2 blue Illusion creature tokens with "Whenever this token blocks a creature, that creature doesn't untap during its controller's next untap step."
This creature has hexproof as long as you control an Illusion.

Polymorphist's Jest

Until end of turn, each creature target player controls loses all abilities and becomes a blue Frog with base power and toughness 1/1.

Serpentine Ambush

Until end of turn, target creature becomes a blue Serpent with base power and toughness 5/5.

Final-Word Phantom

Flash
Flying
During each opponent's end step, you may cast spells as though they had flash.

Elrond, Lord of Rivendell

Whenever Elrond or another creature you control enters, scry 1. If this is the second time this ability has resolved this turn, the Ring tempts you.

Leyline of Anticipation

If this card is in your opening hand, you may begin the game with it on the battlefield.
You may cast spells as though they had flash.

Phyrexian Walker

Stunt Double

Flash
You may have this creature enter as a copy of any creature on the battlefield.

Diminish

Target creature has base power and toughness 1/1 until end of turn.

Saiba Cryptomancer

Flash
Backup 1 (When this creature enters, put a +1/+1 counter on target creature. If that's another creature, it gains the following ability until end of turn.)
Hexproof

High Fae Trickster

Flash (You may cast this spell any time you could cast an instant.)
Flying
You may cast spells as though they had flash.

Aetherplasm

Whenever this creature blocks a creature, you may return this creature to its owner's hand. If you do, you may put a creature card from your hand onto the battlefield blocking that creature.

Brine Hag

When this creature dies, change the base power and toughness of all creatures that dealt damage to it this turn to 0/2. (This effect lasts indefinitely.)

Gift of Tusks

Until end of turn, target creature loses all abilities and becomes a green Elephant with base power and toughness 3/3.

Dream Fighter

Whenever this creature blocks or becomes blocked by a creature, this creature and that creature phase out. (While they're phased out, they're treated as though they don't exist. Each one phases in before its controller untaps during their next untap step.)

Memnite

Sakashima's Student

Ninjutsu {1}{U} ({1}{U}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
You may have this creature enter as a copy of any creature on the battlefield, except it's a Ninja in addition to its other creature types.

Mistblade Shinobi

Ninjutsu {U} ({U}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Whenever this creature deals combat damage to a player, you may return target creature that player controls to its owner's hand.

Faerie Impostor

Flying
When this creature enters, sacrifice it unless you return another creature you control to its owner's hand.

Smoke Bomb

Flash
All creatures have shroud. (They can't be the targets of spells or abilities.)
At the beginning of your upkeep, sacrifice this artifact. When you do, target creature you control can't be blocked this turn.

Aether Channeler

When this creature enters, choose one —
• Create a 1/1 white Bird creature token with flying.
• Return another target nonland permanent to its owner's hand.
• Draw a card.

Thousand-Faced Shadow

Ninjutsu {2}{U}{U} ({2}{U}{U}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Flying
When this creature enters from your hand, if it's attacking, create a token that's a copy of another target attacking creature. The token enters tapped and attacking.

Unstable Shapeshifter

Whenever another creature enters, this creature becomes a copy of that creature, except it has this ability.

Aboleth Spawn

Flash
Ward {2}
Probing Telepathy — Whenever a creature entering under an opponent's control causes a triggered ability of that creature to trigger, you may copy that ability. You may choose new targets for the copy.

Sage of the Falls

Whenever this creature or another non-Human creature you control enters, you may draw a card. If you do, discard a card.

Flatline

Creatures your opponents control have base power and toughness 0/1 until end of turn.

Wall of Tears

Defender (This creature can't attack.)
Whenever this creature blocks a creature, return that creature to its owner's hand at end of combat.

Shape Stealer

Whenever this creature blocks or becomes blocked by a creature, change this creature's base power and toughness to that creature's power and toughness until end of turn.

Ovinize

Until end of turn, target creature loses all abilities and has base power and toughness 0/1.

Shield Sphere

Defender
Whenever this creature blocks, put a -0/-1 counter on it.

The Blue Spirit

You may cast the first creature spell you cast each turn as though it had flash.
Whenever a nontoken creature you control enters during combat, draw a card.

Teferi, Mage of Zhalfir

Flash
Creature cards you own that aren't on the battlefield have flash.
Each opponent can cast spells only any time they could cast a sorcery.

Breath of the Sleepless

You may cast Spirit spells as though they had flash.
Whenever you cast a creature spell during an opponent's turn, tap up to one target creature.

Turn to Frog

Until end of turn, target creature loses all abilities and becomes a blue Frog with base power and toughness 1/1.

Sakashima's Protege

Flash
Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom in a random order.)
You may have this creature enter as a copy of any permanent that entered this turn.

Quickling

Flash (You may cast this spell any time you could cast an instant.)
Flying
When this creature enters, sacrifice it unless you return another creature you control to its owner's hand.

Timid Drake

Flying
When another creature enters, return this creature to its owner's hand.

Serendib Sorcerer

{T}: Target creature other than this creature has base power and toughness 0/2 until end of turn.