Chromium, the Mutable

Flash
This spell can't be countered.
Flying
Discard a card: Until end of turn, Chromium, the Mutable becomes a Human with base power and toughness 1/1, loses all abilities, and gains hexproof. It can't be blocked this turn.

Archivist of Oghma

Flash
Whenever an opponent searches their library, you gain 1 life and draw a card.

Alms Collector

Flash
If an opponent would draw two or more cards, instead you and that player each draw a card.

Aven Mindcensor

Flash
Flying
If an opponent would search a library, that player searches the top four cards of that library instead.

Aboleth Spawn

Flash
Ward {2}
Probing Telepathy — Whenever a creature entering under an opponent's control causes a triggered ability of that creature to trigger, you may copy that ability. You may choose new targets for the copy.