Arbiter of Knollridge

Vigilance
When Arbiter of Knollridge enters, each player's life total becomes the highest life total among all players.

Autumn-Tail, Kitsune Sage

{1}: Attach target Aura attached to a creature to another creature.

Kitsune Mystic

At the beginning of the end step, if Kitsune Mystic is enchanted by two or more Auras, flip it.

Kitsune Mystic // Autumn-Tail, Kitsune Sage

Arcanis the Omnipotent

{T}: Draw three cards.
{2}{U}{U}: Return Arcanis to its owner's hand.

Ambassador Laquatus

Augur of Bolas

When Augur of Bolas enters, look at the top three cards of your library. You may reveal an instant or sorcery card from among them and put it into your hand. Put the rest on the bottom of your library in any order.

Alchemist's Apprentice

Sacrifice Alchemist's Apprentice: Draw a card.

Archetype of Imagination

Creatures you control have flying.
Creatures your opponents control lose flying and can't have or gain flying.

Aether Adept

When Aether Adept enters, return target creature to its owner's hand.

Artisan of Forms

Heroic — Whenever you cast a spell that targets Artisan of Forms, you may have Artisan of Forms become a copy of target creature, except it has this ability.

Arctic Aven

Flying
Arctic Aven gets +1/+1 as long as you control a Plains.
{W}: Arctic Aven gains lifelink until end of turn. (Damage dealt by this creature also causes you to gain that much life.)

Augury Adept

Whenever Augury Adept deals combat damage to a player, reveal the top card of your library and put that card into your hand. You gain life equal to its mana value.

Aven Augur

Flying
Sacrifice Aven Augur: Return up to two target creatures to their owners' hands. Activate only during your upkeep.