Mentor of the Meek

Whenever another creature you control with power 2 or less enters, you may pay {1}. If you do, draw a card.

Haunted Library

Whenever a creature an opponent controls dies, you may pay {1}. If you do, create a 1/1 white Spirit creature token with flying.

Imposing Grandeur

Each player may discard their hand and draw cards equal to the greatest mana value of a commander they own on the battlefield or in the command zone.

Arterial Alchemy

When Arterial Alchemy enters, create a Blood token for each opponent you have. (It's an artifact with "{1}, {T}, Discard a card, Sacrifice this artifact: Draw a card.")
Blood tokens you control are Equipment in addition to their other types and have "Equipped creature gets +2/+0" and equip {2}.

Bloodsworn Steward

Flying
Commander creatures you control get +2/+2 and have haste.

Knight of the White Orchid

First strike
When Knight of the White Orchid enters, if an opponent controls more lands than you, you may search your library for a Plains card, put it onto the battlefield, then shuffle.

Windborn Muse

Flying
Creatures can't attack you unless their controller pays {2} for each creature they control that's attacking you.