Contortionist Troupe

Contortionist Troupe enters with X +1/+1 counters on it.
Coven — At the beginning of your end step, if you control three or more creatures with different powers, put a +1/+1 counter on target creature you control.

Brainstealer Dragon

Flying
At the beginning of your end step, exile the top card of each opponent's library. You may play those cards for as long as they remain exiled. If you cast a spell this way, you may spend mana as though it were mana of any color to cast it.
Whenever a nonland permanent an opponent owns enters the battlefield under your control, they lose life equal to its mana value.

Boot Nipper

Boot Nipper enters with your choice of a deathtouch counter or a lifelink counter on it.

Druid Class

(Gain the next level as a sorcery to add its ability.)
Landfall — Whenever a land you control enters, you gain 1 life.
{2}{G}: Level 2
You may play an additional land on each of your turns.
{4}{G}: Level 3
When this Class becomes level 3, target land you control becomes a creature with haste and "This creature's power and toughness are each equal to the number of lands you control." It's still a land.

Avenger of Zendikar

When Avenger of Zendikar enters, create a 0/1 green Plant creature token for each land you control.
Landfall — Whenever a land you control enters, you may put a +1/+1 counter on each Plant creature you control.

Doomwake Giant

Constellation — Whenever Doomwake Giant or another enchantment you control enters, creatures your opponents control get -1/-1 until end of turn.

Grizzly Ghoul

Trample
Grizzly Ghoul enters with a +1/+1 counter on it for each creature that died this turn.

Yarok, the Desecrated

Deathtouch, lifelink
If a permanent entering causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.

Sadistic Glee

Enchant creature
Whenever a creature dies, put a +1/+1 counter on enchanted creature.

Archfiend of the Dross

Flying
Archfiend of the Dross enters with four oil counters on it.
At the beginning of your upkeep, remove an oil counter from Archfiend of the Dross. Then if it has no oil counters on it, you lose the game.
Whenever a creature an opponent controls dies, its controller loses 2 life.

Ayara, First of Locthwain

Whenever Ayara, First of Locthwain or another black creature you control enters, each opponent loses 1 life and you gain 1 life.
{T}, Sacrifice another black creature: Draw a card.

Curse of the Restless Dead

Enchant player
Whenever a land enchanted player controls enters, you create a 2/2 black Zombie creature token with decayed. (It can't block. When it attacks, sacrifice it at end of combat.)

Champion of Lambholt

Creatures with power less than Champion of Lambholt's power can't block creatures you control.
Whenever another creature you control enters, put a +1/+1 counter on Champion of Lambholt.

Bloatfly Swarm

Flying
Bloatfly Swarm enters with five +1/+1 counters on it.
If damage would be dealt to Bloatfly Swarm while it has a +1/+1 counter on it, prevent that damage, remove that many +1/+1 counters from it, then give each player a rad counter for each +1/+1 counter removed this way.

Carth the Lion

Whenever Carth the Lion enters or a planeswalker you control dies, look at the top seven cards of your library. You may reveal a planeswalker card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.
Planeswalkers' loyalty abilities you activate cost an additional [+1] to activate.

Gristle Grinner

Whenever a creature dies, Gristle Grinner gets +2/+2 until end of turn.

Bioessence Hydra

Trample
Bioessence Hydra enters with a +1/+1 counter on it for each loyalty counter on planeswalkers you control.
Whenever one or more loyalty counters are put on planeswalkers you control, put that many +1/+1 counters on Bioessence Hydra.

Elrond, Lord of Rivendell

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

Garruk's Uprising

When Garruk's Uprising enters, if you control a creature with power 4 or greater, draw a card.
Creatures you control have trample.
Whenever a creature you control with power 4 or greater enters, draw a card.

Fell Beast of Mordor

Flying
Devour 1 (As this enters, you may sacrifice any number of creatures. This creature enters with that many +1/+1 counters on it.)
Whenever Fell Beast of Mordor enters or attacks, target opponent loses X life and you gain X life, where X is the number of +1/+1 counters on it.

Combine Guildmage

{1}{G}, {T}: This turn, each creature you control enters with an additional +1/+1 counter on it.
{1}{U}, {T}: Move a +1/+1 counter from target creature you control onto another target creature you control.

Bloodcrazed Paladin

Flash
Bloodcrazed Paladin enters with a +1/+1 counter on it for each creature that died this turn.

Garruk's Packleader

Whenever another creature you control with power 3 or greater enters, you may draw a card.

Composer of Spring

Constellation — Whenever an enchantment you control enters, you may put a land card from your hand onto the battlefield tapped. If you control six or more enchantments, instead you may put a creature or land card from your hand onto the battlefield tapped.

Baloth Woodcrasher

Landfall — Whenever a land you control enters, Baloth Woodcrasher gets +4/+4 and gains trample until end of turn. (It can deal excess combat damage to the player or planeswalker it's attacking.)

Evolution Sage

Landfall — Whenever a land you control enters, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Gala Greeters

Alliance — Whenever another creature you control enters, choose one that hasn't been chosen this turn —
• Put a +1/+1 counter on Gala Greeters.
• Create a tapped Treasure token.
• You gain 2 life.

Dreadhound

When Dreadhound enters, mill three cards. (Put the top three cards of your library into your graveyard.)
Whenever a creature dies or a creature card is put into a graveyard from a library, each opponent loses 1 life.

Black Market

Whenever a creature dies, put a charge counter on Black Market.
At the beginning of your first main phase, add {B} for each charge counter on Black Market.

Daxos's Torment

Constellation — Whenever Daxos's Torment or another enchantment you control enters, Daxos's Torment becomes a 5/5 Demon creature with flying and haste in addition to its other types until end of turn.

Eidolon of Blossoms

Constellation — Whenever Eidolon of Blossoms or another enchantment you control enters, draw a card.

Attended Socialite

Alliance — Whenever another creature you control enters, Attended Socialite gets +1/+1 until end of turn.

Blood Seeker

Whenever a creature an opponent controls enters, you may have that player lose 1 life.