Bookwurm

Trample
When Bookwurm enters, you gain 3 life and draw a card.
{2}{G}: Put Bookwurm from your graveyard into your library third from the top.

Kor Celebrant

Whenever Kor Celebrant or another creature you control enters, you gain 1 life.

Trostani, Selesnya's Voice

Whenever another creature you control enters, you gain life equal to that creature's toughness.
{1}{G}{W}, {T}: Populate. (Create a token that's a copy of a creature token you control.)

Auriok Champion

Protection from black and from red
Whenever another creature enters, you may gain 1 life.

Ageless Entity

Whenever you gain life, put that many +1/+1 counters on Ageless Entity.

Soul Warden

Whenever another creature enters, you gain 1 life.

Inspiring Overseer

Flying
When this creature enters, you gain 1 life and draw a card.

Circuit Mender

When Circuit Mender enters, you gain 2 life.
When Circuit Mender leaves the battlefield, draw a card.

Blossoming Bogbeast

Whenever Blossoming Bogbeast attacks, you gain 2 life. Then creatures you control gain trample and get +X/+X until end of turn, where X is the amount of life you gained this turn.

Loxodon Lifechanter

When Loxodon Lifechanter enters, you may have your life total become the total toughness of creatures you control.
{5}{W}: Loxodon Lifechanter gets +X/+X until end of turn, where X is your life total.

Luminate Primordial

Vigilance
When Luminate Primordial enters, for each opponent, exile up to one target creature that player controls and that player gains life equal to its power.

Roon of the Hidden Realm

Vigilance, trample
{2}, {T}: Exile another target creature. Return that card to the battlefield under its owner's control at the beginning of the next end step.

Soul's Attendant

Whenever another creature enters, you may gain 1 life.

Essence Warden

Angel of Grace

Flash
Flying
When Angel of Grace enters, until end of turn, damage that would reduce your life total to less than 1 reduces it to 1 instead.
{4}{W}{W}, Exile Angel of Grace from your graveyard: Your life total becomes 10.

Dwarven Priest

When Dwarven Priest enters, you gain 1 life for each creature you control.

Prosperous Innkeeper

When Prosperous Innkeeper enters, create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")
Whenever another creature you control enters, you gain 1 life.

Cloudblazer

Flying
When this creature enters, you gain 2 life and draw two cards.

Titan of Industry

Reach, trample
When Titan of Industry enters, choose two —
• Destroy target artifact or enchantment.
• Target player gains 5 life.
• Create a 4/4 green Rhino Warrior creature token.
• Put a shield counter on a creature you control.

Ancestor's Chosen

First strike (This creature deals combat damage before creatures without first strike.)
When Ancestor's Chosen enters, you gain 1 life for each card in your graveyard.

Speakeasy Server

Flying
When Speakeasy Server enters, you gain 1 life for each other creature you control.

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.

Angel of Renewal

Flying
When Angel of Renewal enters, you gain 1 life for each creature you control.

Healer of the Pride

Whenever another creature you control enters, you gain 2 life.

Verdant Sun's Avatar

Whenever Verdant Sun's Avatar or another creature you control enters, you gain life equal to that creature's toughness.

Archangel of Thune

Flying
Lifelink (Damage dealt by this creature also causes you to gain that much life.)
Whenever you gain life, put a +1/+1 counter on each creature you control.

Thragtusk

When Thragtusk enters, you gain 5 life.
When Thragtusk leaves the battlefield, create a 3/3 green Beast creature token.