Sai, Master Thopterist

Whenever you cast an artifact spell, create a 1/1 colorless Thopter artifact creature token with flying.
{1}{U}, Sacrifice two artifacts: Draw a card.

Aetherflux Reservoir

Whenever you cast a spell, you gain 1 life for each spell you've cast this turn.
Pay 50 life: Aetherflux Reservoir deals 50 damage to any target.

Aeolipile

{1}, {T}, Sacrifice Aeolipile: It deals 2 damage to any target.

Amulet of Vigor

Whenever a permanent you control enters tapped, untap it.

Altar of the Lost

Altar of the Lost enters tapped.
{T}: Add two mana in any combination of colors. Spend this mana only to cast spells with flashback from a graveyard.

Arcbound Fiend

Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)
At the beginning of your upkeep, you may move a +1/+1 counter from target creature onto Arcbound Fiend.
Modular 3 (This creature enters with three +1/+1 counters on it. When it dies, you may put its +1/+1 counters on target artifact creature.)

Angelheart Vial

Whenever you're dealt damage, you may put that many charge counters on Angelheart Vial.
{2}, {T}, Remove four charge counters from Angelheart Vial: You gain 2 life and draw a card.

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Aeon Engine

Aeon Engine enters tapped.
{T}, Exile Aeon Engine: Reverse the game's turn order. (For example, if play had proceeded clockwise around the table, it now goes counterclockwise.)

Angel's Tomb

Whenever a creature you control enters, you may have Angel's Tomb become a 3/3 white Angel artifact creature with flying until end of turn.

Arcbound Lancer

First strike
Modular 4 (This creature enters with four +1/+1 counters on it. When it dies, you may put its +1/+1 counters on target artifact creature.)

Arcbound Overseer

At the beginning of your upkeep, put a +1/+1 counter on each creature you control with modular.
Modular 6 (This creature enters with six +1/+1 counters on it. When it dies, you may put its +1/+1 counters on target artifact creature.)

Arcane Encyclopedia

Altar Golem

Trample
Altar Golem's power and toughness are each equal to the number of creatures on the battlefield.
Altar Golem doesn't untap during your untap step.
Tap five untapped creatures you control: Untap Altar Golem.