Viscera Seer

Sacrifice a creature: Scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Scholar of New Horizons

This creature enters with a +1/+1 counter on it.
{T}, Remove a counter from a permanent you control: Search your library for a Plains card and reveal it. If an opponent controls more lands than you, you may put that card onto the battlefield tapped. If you don't put the card onto the battlefield, put it into your hand. Then shuffle.

Luminous Broodmoth

Flying
Whenever a creature you control without flying dies, return it to the battlefield under its owner's control with a flying counter on it.

Isilu, Carrier of Twilight

Flying, lifelink
Each other nontoken creature you control has persist. (When it dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)
At the beginning of your first main phase, you may pay {W}. If you do, transform Isilu.

Eirdu, Carrier of Dawn

Flying, lifelink
Creature spells you cast have convoke. (Your creatures can help cast those spells. Each creature you tap while casting a creature spell pays for {1} or one mana of that creature's color.)
At the beginning of your first main phase, you may pay {B}. If you do, transform Eirdu.

Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight

Warren Soultrader

Pay 1 life, Sacrifice another creature: Create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

Summon: Knights of Round

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after V.)
I, II, III, IV — Create three 2/2 white Knight creature tokens.
V — Ultimate End — Other creatures you control get +2/+2 until end of turn. Put an indestructible counter on each of them.
Indestructible

Oketra's Monument

White creature spells you cast cost {1} less to cast.
Whenever you cast a creature spell, create a 1/1 white Warrior creature token with vigilance.

Carrion Feeder

This creature can't block.
Sacrifice a creature: Put a +1/+1 counter on this creature.

Umbral Collar Zealot

Sacrifice another creature or artifact: Surveil 1. (Look at the top card of your library. You may put it into your graveyard.)

Mikaeus, the Unhallowed

Intimidate (This creature can't be blocked except by artifact creatures and/or creatures that share a color with it.)
Whenever a Human deals damage to you, destroy it.
Other non-Human creatures you control get +1/+1 and have undying. (When a creature with undying dies, if it had no +1/+1 counters on it, return it to the battlefield under its owner's control with a +1/+1 counter on it.)