Tokka & Rahzar, Terrible Twos

This spell can't be countered.
Menace
Whenever a player casts a spell, if the amount of mana spent to cast it was less than its mana value, Tokka & Rahzar deal 3 damage to that player.

Rocksteady, Mutant Marauder

Partner with Bebop, Skull & Crossbones (When this creature enters, target player may put Bebop into their hand from their library, then shuffle.)
Trample
Whenever another nontoken creature you control enters, put a +1/+1 counter on target creature.

Corpsejack Menace

If one or more +1/+1 counters would be put on a creature you control, twice that many +1/+1 counters are put on it instead.

Leatherhead, Iron Gator

Trample, haste
Whenever Leatherhead attacks, put two +1/+1 counters on each creature you control.

Slash, Reptile Rampager

Alliance — Whenever another creature you control enters, Slash deals 2 damage to each opponent.
Whenever Slash attacks, create a 2/2 red Mutant creature token.

Groundchuck & Dirtbag

Trample
Whenever you tap a land for mana, add {G}.

Primordial Pachyderm

Reach, trample
When this creature enters, you gain 2 life.

Vigor

Trample
If damage would be dealt to another creature you control, prevent that damage. Put a +1/+1 counter on that creature for each 1 damage prevented this way.
When Vigor is put into a graveyard from anywhere, shuffle it into its owner's library.

Tenderize

Target creature you control deals damage equal to its power to target creature an opponent controls.

Putrid Pals

Deathtouch
Disappear — This creature enters with two +1/+1 counters on it if a permanent left the battlefield under your control this turn.

Bebop, Warthog Warrior

Menace (This creature can't be blocked except by two or more creatures.)
Rhinos you control have menace.
Swampcycling {2} ({2}, Discard this card: Search your library for a Swamp card, reveal it, put it into your hand, then shuffle.)

Tokka & Rahzar, Unsupervised

First strike
Whenever another nontoken creature you control leaves the battlefield, put a +1/+1 counter on Tokka & Rahzar and create a Treasure token. This ability triggers only once each turn.

Bebop, Skull & Crossbones

Partner with Rocksteady, Mutant Marauder (When this creature enters, target player may put Rocksteady into their hand from their library, then shuffle.)
Deathtouch
Whenever Bebop deals combat damage to a player, you may draw X cards, where X is the number of counters on Bebop. If you do, you lose X life.

Rocksteady, Crash Courser

Rocksteady can't be blocked by more than one creature.
Boars you control can't be blocked by more than one creature.
Forestcycling {2} ({2}, Discard this card: Search your library for a Forest card, reveal it, put it into your hand, then shuffle.)

Pizza Face, Gastromancer

When Pizza Face enters, create a Food token.
Disappear — At the beginning of your end step, if a permanent left the battlefield under your control this turn, put three +1/+1 counters on up to one other target artifact or creature. If it isn't a creature, it becomes a 0/0 Mutant creature in addition to its other types.
{10}, {T}, Sacrifice Pizza Face: You gain 15 life.

Bebop & Rocksteady

Whenever Bebop & Rocksteady attack or block, sacrifice a permanent unless you discard a card.

Mole Module

Menace
Whenever this Vehicle deals combat damage to a player, mill four cards. You may put a permanent card from among them onto the battlefield.
Crew 2

Leatherhead, Swamp Stalker

Trample
Leatherhead enters with a hexproof counter on her.
Whenever Leatherhead deals combat damage to a player, you may remove a counter from her. When you do, destroy target artifact or enchantment that player controls.

Slithering Cryptid

When this creature enters, create a Mutagen token. (It's an artifact with "{1}, {T}, Sacrifice this token: Put a +1/+1 counter on target creature. Activate only as a sorcery.")

Old Hob, Alleycat Blues

At the beginning of combat on your turn, create a 2/2 red Mutant creature token. It gains haste until end of turn. Destroy it at the beginning of the next end step.
{1}{W}: Target attacking creature token gains indestructible until end of turn.

Monster Mashup

Reach (This creature can block creatures with flying.)
Menace (This creature can't be blocked except by two or more creatures.)

Wingnut, Bat on the Belfry

Alliance — Whenever another creature you control enters, Wingnut gains your choice of flying, menace, or haste until end of turn.
Whenever Wingnut attacks, each other attacking creature gets +1/+0 until end of turn.

Lord Dregg, Insect Invader

Flying
Disappear — At the beginning of your end step, if a permanent left the battlefield under your control this turn, create a 1/1 black Insect Warrior creature token with flying.
{3}{G}, Sacrifice a token: Draw a card.