Cut Your Losses

Casualty 2 (As you cast this spell, you may sacrifice a creature with power 2 or greater. When you do, copy this spell and you may choose a new target for the copy.)
Target player mills half their library, rounded down.

Galloping Lizrog

Trample
When Galloping Lizrog enters, you may remove any number of +1/+1 counters from among creatures you control. If you do, put twice that many +1/+1 counters on Galloping Lizrog.

Masked Vandal

Changeling (This card is every creature type.)
When Masked Vandal enters, you may exile a creature card from your graveyard. If you do, exile target artifact or enchantment an opponent controls.

Grolnok, the Omnivore

Whenever a Frog you control attacks, mill three cards.
Whenever a permanent card is put into your graveyard from your library, exile it with a croak counter on it.
You may play lands and cast spells from among cards you own in exile with croak counters on them.

Laboratory Maniac

If you would draw a card while your library has no cards in it, you win the game instead.

Millikin

{T}, Mill a card: Add {C}. (To mill a card, put the top card of your library into your graveyard.)

Excavating Anurid

When Excavating Anurid enters, you may sacrifice a land. If you do, draw a card.
Threshold — As long as seven or more cards are in your graveyard, Excavating Anurid gets +1/+1 and has vigilance.

Froghemoth

Trample, haste
Whenever Froghemoth deals combat damage to a player, exile up to that many target cards from their graveyard. Put a +1/+1 counter on Froghemoth for each creature card exiled this way. You gain 1 life for each noncreature card exiled this way.

Slogurk, the Overslime

Trample
Whenever a land card is put into your graveyard from anywhere, put a +1/+1 counter on Slogurk, the Overslime.
Remove three +1/+1 counters from Slogurk: Return it to its owner's hand.
When Slogurk leaves the battlefield, return up to three target land cards from your graveyard to your hand.

Cephalid Illusionist

Whenever Cephalid Illusionist becomes the target of a spell or ability, mill three cards.
{2}{U}, {T}: Prevent all combat damage that would be dealt to and dealt by target creature you control this turn.

Llanowar Elves

Jade Avenger

Bushido 2 (Whenever this creature blocks or becomes blocked, it gets +2/+2 until end of turn.)

Sakura-Tribe Elder

Sacrifice Sakura-Tribe Elder: Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Murkfiend Liege

Other green creatures you control get +1/+1.
Other blue creatures you control get +1/+1.
Untap all green and/or blue creatures you control during each other player's untap step.

Satyr Wayfinder

When Satyr Wayfinder enters, reveal the top four cards of your library. You may put a land card from among them into your hand. Put the rest into your graveyard.

Court of Cunning

When Court of Cunning enters, you become the monarch.
At the beginning of your upkeep, any number of target players each mill two cards. If you're the monarch, each of those players mills ten cards instead. (To mill a card, a player puts the top card of their library into their graveyard.)

Frogify

Enchant creature
Enchanted creature loses all abilities and is a blue Frog creature with base power and toughness 1/1. (It loses all other card types and creature types.)

Haze Frog

Flash (You may cast this spell any time you could cast an instant.)
When Haze Frog enters, prevent all combat damage that other creatures would deal this turn.

Frogmite

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)

Plaxcaster Frogling

Graft 3 (This creature enters with three +1/+1 counters on it. Whenever another creature enters, you may move a +1/+1 counter from this creature onto it.)
{2}: Target creature with a +1/+1 counter on it gains shroud until end of turn. (It can't be the target of spells or abilities.)

Counterspell

Willow Geist

Trample
Whenever one or more cards leave your graveyard, put a +1/+1 counter on Willow Geist.
When Willow Geist dies, you gain life equal to its power.

Elvish Mystic

Mana Drain

Counter target spell. At the beginning of your next main phase, add an amount of {C} equal to that spell's mana value.

Negate

Traumatize

Target player mills half their library, rounded down.

Chub Toad

Whenever Chub Toad blocks or becomes blocked, it gets +2/+2 until end of turn.

Hedron Crab

Landfall — Whenever a land you control enters, target player mills three cards.

Burrog Befuddler

Flash
When Burrog Befuddler enters, target creature an opponent controls gets -1/-0 until end of turn.

Consider

Surveil 1. (Look at the top card of your library. You may put it into your graveyard.)
Draw a card.

Mystic Snake

Flash
When Mystic Snake enters, counter target spell.

Boseiju, Who Endures

{T}: Add {G}.
Channel — {1}{G}, Discard Boseiju, Who Endures: Destroy target artifact, enchantment, or nonbasic land an opponent controls. That player may search their library for a land card with a basic land type, put it onto the battlefield, then shuffle. This ability costs {1} less to activate for each legendary creature you control.

Lightning Greaves

Equipped creature has haste and shroud. (It can't be the target of spells or abilities.)
Equip {0}

Leapfrog

Leapfrog has flying as long as you've cast an instant or sorcery spell this turn.

Perpetual Timepiece

{T}: Mill two cards.
{2}, Exile Perpetual Timepiece: Shuffle any number of target cards from your graveyard into your library.

Reclamation Sage

When Reclamation Sage enters, you may destroy target artifact or enchantment.

Thought Scour

Target player mills two cards.
Draw a card.

Whiptongue Frog

{U}: Whiptongue Frog gains flying until end of turn.

Turn to Frog

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

Bloated Toad

Protection from blue
Cycling {2} ({2}, Discard this card: Draw a card.)

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Dispel

Deranged Assistant

Otherworldly Gaze

Surveil 3. (Look at the top three cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)
Flashback {1}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Talisman of Curiosity

{T}: Add {C}.
{T}: Add {G} or {U}. Talisman of Curiosity deals 1 damage to you.

Witness Protection

Enchant creature
Enchanted creature loses all abilities and is a green and white Citizen creature with base power and toughness 1/1 named Legitimate Businessperson. (It loses all other colors, card types, creature types, and names.)

Fleet Swallower

Whenever Fleet Swallower attacks, target player mills half their library, rounded up.

Jace, Wielder of Mysteries

If you would draw a card while your library has no cards in it, you win the game instead.
+1: Target player mills two cards. Draw a card.
−8: Draw seven cards. Then if your library has no cards in it, you win the game.

Fyndhorn Elves

Steeple Creeper

{3}{U}: Steeple Creeper gains flying until end of turn.

Papercraft Decoy

When Papercraft Decoy leaves the battlefield, you may pay {2}. If you do, draw a card.

Sol Ring

Spore Frog

Sacrifice Spore Frog: Prevent all combat damage that would be dealt this turn.

Otawara, Soaring City

{T}: Add {U}.
Channel — {3}{U}, Discard Otawara, Soaring City: Return target artifact, creature, enchantment, or planeswalker to its owner's hand. This ability costs {1} less to activate for each legendary creature you control.

Crocanura

Reach (This creature can block creatures with flying.)
Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)

Omnibian

{T}: Target creature becomes a Frog with base power and toughness 3/3 until end of turn.

Trollbred Guardian

{2}{G}: Adapt 2. (If this creature has no +1/+1 counters on it, put two +1/+1 counters on it.)
Each creature you control with a +1/+1 counter on it has trample.

Rapid Hybridization

Destroy target creature. It can't be regenerated. That creature's controller creates a 3/3 green Frog Lizard creature token.

Growth Spiral

Draw a card. You may put a land card from your hand onto the battlefield.

Swiftfoot Boots

Equipped creature has hexproof and haste. (It can't be the target of spells or abilities your opponents control.)
Equip {1}

Croaking Counterpart

Create a token that's a copy of target non-Frog creature, except it's a 1/1 green Frog.
Flashback {3}{G}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)