Mentor of the Meek

Whenever another creature you control with power 2 or less enters, you may pay {1}. If you do, draw a card.

Soul Warden

Whenever another creature enters, you gain 1 life.

Radiant Solar

Flying, lifelink
Whenever this creature or another nontoken creature you control enters, venture into the dungeon. (Enter the first room or advance to the next room.)
{W}, Discard this card: Venture into the dungeon and you gain 3 life.

Guide of Souls

Whenever another creature you control enters, you gain 1 life and get {E} (an energy counter).
Whenever you attack, you may pay {E}{E}{E}. When you do, put two +1/+1 counters and a flying counter on target attacking creature. It becomes an Angel in addition to its other types.

Loran, Disciple of History

Whenever Loran or another legendary creature you control enters, return target artifact card from your graveyard to your hand.

Preston, the Vanisher

Whenever another nontoken creature you control enters, if it wasn't cast, create a token that's a copy of that creature, except it's a 0/1 white Illusion.
{1}{W}, Sacrifice five Illusions: Exile target nonland permanent.

Pandemonium

Whenever a creature enters, that creature's controller may have it deal damage equal to its power to any target of their choice.

Mana Echoes

Whenever a creature enters, you may add an amount of {C} equal to the number of creatures you control that share a creature type with it.

Authority of the Consuls

Creatures your opponents control enter tapped.
Whenever a creature an opponent controls enters, you gain 1 life.

Saradoc, Master of Buckland

Whenever Saradoc or another nontoken creature you control with power 2 or less enters, create a 1/1 white Halfling creature token.
Tap two other untapped Halflings you control: Saradoc gets +2/+0 and gains lifelink until end of turn.

Rumor Gatherer

Alliance — Whenever another creature you control enters, scry 1. If this is the second time this ability has resolved this turn, draw a card instead.

Soul's Attendant

Whenever another creature enters, you may gain 1 life.

Suture Priest

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

Gimli of the Glittering Caves

Double strike
Whenever another legendary creature you control enters, put a +1/+1 counter on Gimli.
Whenever Gimli deals combat damage to a player, create a Treasure token.

Park Bleater

Whenever another creature you own enters, you get {TK}.
{W}, {T}: You may put a sticker on a creature you own that entered this turn.

Cream of the Crop

Whenever a creature you control enters, you may look at the top X cards of your library, where X is that creature's power. If you do, put one of those cards on top of your library and the rest on the bottom of your library in any order.

Genesis Chamber

Whenever a nontoken creature enters, if this artifact is untapped, that creature's controller creates a 1/1 colorless Myr artifact creature token.

Rose Room Treasurer

Alliance — Whenever another creature you control enters, create a Treasure token if this is the first or second time this ability has resolved this turn. Otherwise, you may pay {X}. When you do, this creature deals X damage to any target.

Metastatic Evangel

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

Saltskitter

Whenever another creature enters, exile this creature. Return this creature to the battlefield under its owner's control at the beginning of the next end step.

Legolas Greenleaf

Reach
Legolas can't be blocked by creatures with power 2 or less.
Whenever another legendary creature you control enters, put a +1/+1 counter on Legolas.
Whenever Legolas deals combat damage to a player, draw a card.

Soul of the Harvest

Trample
Whenever another nontoken creature you control enters, you may draw a card.

Rosie Cotton of South Lane

When Rosie Cotton enters, create a Food token. (It's an artifact with "{2}, {T}, Sacrifice this token: You gain 3 life.")
Whenever you create a token, put a +1/+1 counter on target creature you control other than Rosie Cotton.

Lossarnach Captain

First strike
Whenever this creature or another Human you control enters, tap target creature an opponent controls.
At the beginning of your upkeep, create a 1/1 white Human Soldier creature token.

Samwise Gamgee

Whenever another nontoken creature you control enters, create a Food token. (It's an artifact with "{2}, {T}, Sacrifice this token: You gain 3 life.")
Sacrifice three Foods: Return target historic card from your graveyard to your hand. (Artifacts, legendaries, and Sagas are historic.)

Irreverent Gremlin

Menace (This creature can't be blocked except by two or more creatures.)
Whenever another creature you control with power 2 or less enters, you may discard a card. If you do, draw a card. Do this only once each turn.