Obsidian Battle-Axe

Equipped creature gets +2/+1 and has haste.
Whenever a Warrior creature enters, you may attach Obsidian Battle-Axe to it.
Equip {3}

Rush of Battle

Creatures you control get +2/+1 until end of turn. Warrior creatures you control gain lifelink until end of turn. (Damage dealt by those Warriors also causes their controller to gain that much life.)

God-Eternal Oketra

Double strike
Whenever you cast a creature spell, create a 4/4 black Zombie Warrior creature token with vigilance.
When God-Eternal Oketra dies or is put into exile from the battlefield, you may put it into its owner's library third from the top.

Mummy Paramount

Whenever another Zombie you control enters, Mummy Paramount gets +1/+1 until end of turn.

Binding Mummy

Whenever another Zombie you control enters, you may tap target artifact or creature.

Time to Reflect

Exile target creature that blocked or was blocked by a Zombie this turn.

Soul's Attendant

Whenever another creature enters, you may gain 1 life.

Securitron Squadron

Squad {3} (As an additional cost to cast this spell, you may pay {3} any number of times. When this creature enters, create that many tokens that are copies of it.)
Vigilance
Whenever a creature token you control enters, put a +1/+1 counter on it.

Arashin Foremost

Double strike
Whenever Arashin Foremost enters or attacks, another target Warrior creature you control gains double strike until end of turn.

Soul Warden

Whenever another creature enters, you gain 1 life.

Boss's Chauffeur

Boss's Chauffeur enters with a number of +1/+1 counters on it equal to one plus the number of other creatures you control.
Alliance — Whenever another creature you control enters, put a +1/+1 counter on Boss's Chauffeur.
When Boss's Chauffeur dies, create a 1/1 green and white Citizen creature token for each +1/+1 counter on it.

In Oketra's Name

Zombies you control get +2/+1 until end of turn. Other creatures you control get +1/+1 until end of turn.

Tax Collector

When Tax Collector enters, choose one —
• Tax — Until your next turn, spells your opponents cast cost {1} more to cast.
• Arrest — Detain target creature an opponent controls. (Until your next turn, that creature can't attack or block and its activated abilities can't be activated.)

Charismatic Conqueror

Vigilance
Whenever an artifact or creature an opponent controls enters untapped, they may tap that permanent. If they don't, you create a 1/1 white Vampire creature token with lifelink.

Mardu Woe-Reaper

Whenever Mardu Woe-Reaper or another Warrior you control enters, you may exile target creature card from a graveyard. If you do, you gain 1 life.

Unconventional Tactics

Target creature gets +3/+3 and gains flying until end of turn.
Whenever a Zombie you control enters, you may pay {W}. If you do, return Unconventional Tactics from your graveyard to your hand.

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.

Resolute Strike

Target creature gets +2/+2 until end of turn. If it's a Warrior, you may attach an Equipment you control to it.

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.

Cathars' Crusade

Whenever a creature you control enters, put a +1/+1 counter on each creature you control.

Mondrak, Glory Dominus

If one or more tokens would be created under your control, twice that many of those tokens are created instead.
{1}{W/P}{W/P}, Sacrifice two other artifacts and/or creatures: Put an indestructible counter on Mondrak, Glory Dominus. ({W/P} can be paid with either {W} or 2 life.)

Anointer Priest

Whenever a creature token you control enters, you gain 1 life.
Embalm {3}{W} ({3}{W}, Exile this card from your graveyard: Create a token that's a copy of it, except it's a white Zombie Human Cleric with no mana cost. Embalm only as a sorcery.)

Whitemane Lion

Flash
When Whitemane Lion enters, return a creature you control to its owner's hand.