Roman Tishenin

Each plaguebearer is formed from the blighted soul of a mortal slain by Nurgle's Rot.

Nurgle's Rot

Enchant creature an opponent controls
When enchanted creature dies, return Nurgle's Rot to its owner's hand and you create a 1/3 black Demon creature token named Plaguebearer of Nurgle.

The Horus Heresy

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — For each opponent, gain control of up to one target nonlegendary creature that player controls for as long as The Horus Heresy remains on the battlefield.
II — Draw a card for each creature you control but don't own.
III — Starting with you, each player chooses a creature. Destroy each creature chosen this way.

The arcane sphere that hovers near Magnus's staff imbues it with the power to transform enemies into mindless chaos spawn.

Commander's Sphere

{T}: Add one mana of any color in your commander's color identity.
Sacrifice Commander's Sphere: Draw a card.

"The ancient Necron race has achieved this pinnacle of elegance through their relentless pursuit of utility."
—Tech-Priest Darvin, executed for heresy 1256998.M41

Gilded Lotus

Mask of Memory

Whenever equipped creature deals combat damage to a player, you may draw two cards. If you do, discard a card.
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)