Social Climber

Alliance — Whenever another creature you control enters, you gain 1 life.

Luminous Phantom

Flying
Whenever another creature you control leaves the battlefield, you gain 1 life.
If Luminous Phantom would be put into a graveyard from anywhere, exile it instead.

Lunarch Veteran

Whenever another creature you control enters, you gain 1 life.
Disturb {1}{W} (You may cast this card from your graveyard transformed for its disturb cost.)

Lunarch Veteran // Luminous Phantom

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.)

Lurking Roper

Lurking Roper doesn't untap during your untap step.
Whenever you gain life, untap Lurking Roper.

Impassioned Orator

Whenever another creature you control enters, you gain 1 life.

Midnight Guard

Whenever another creature enters, untap Midnight Guard.

Presence of Gond

Enchant creature
Enchanted creature has "{T}: Create a 1/1 green Elf Warrior creature token."

Famished Paladin

Famished Paladin doesn't untap during your untap step.
Whenever you gain life, untap Famished Paladin.