Armageddon Clock

At the beginning of your upkeep, put a doom counter on this artifact.
At the beginning of your draw step, this artifact deals damage equal to the number of doom counters on it to each player.
{4}: Remove a doom counter from this artifact. Any player may activate this ability but only during any upkeep step.

Atraxa, Praetors' Voice

Flying, vigilance, deathtouch, lifelink
At the beginning of your end step, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Walking Skyscraper

This spell costs {1} less to cast for each modified creature you control. (Equipment, Auras you control, and counters are modifications.)
Trample
This creature has hexproof as long as it's untapped. (It can't be the target of spells or abilities your opponents control.)

Pearl-Ear, Imperial Advisor

Lifelink
Enchantment spells you cast have affinity for Auras. (They cost {1} less to cast for each Aura you control.)
Whenever you cast an Aura spell that targets a modified permanent you control, draw a card. (Equipment, Auras you control, and counters are modifications.)

Athreos, Shroud-Veiled

Indestructible
As long as your devotion to white and black is less than seven, Athreos isn't a creature.
At the beginning of your end step, put a coin counter on another target creature.
Whenever a creature with a coin counter on it dies or is put into exile, return that card to the battlefield under your control.

Beastmaster Ascension

Whenever a creature you control attacks, you may put a quest counter on this enchantment.
As long as this enchantment has seven or more quest counters on it, creatures you control get +5/+5.

Blood Curdle

Destroy target creature. Put a menace counter on a creature you control. (It can't be blocked except by two or more creatures.)

Brain in a Jar

{1}, {T}: Put a charge counter on this artifact, then you may cast an instant or sorcery spell with mana value equal to the number of charge counters on this artifact from your hand without paying its mana cost.
{3}, {T}, Remove X charge counters from this artifact: Scry X.

Angelic Sleuth

Flying
Whenever another permanent you control leaves the battlefield, if it had counters on it, investigate. (Create a Clue artifact token with "{2}, Sacrifice this token: Draw a card.")

Boon of Safety

Put a shield counter on target creature. (If it would be dealt damage or destroyed, remove a shield counter from it instead.)
Scry 1.

Envoy of the Ancestors

Outlast {W} ({W}, {T}: Put a +1/+1 counter on this creature. Outlast only as a sorcery.)
Modified creatures you control have lifelink. (Equipment, Auras you control, and counters are modifications.)

Kodama of the West Tree

Reach
Modified creatures you control have trample. (Equipment, Auras you control, and counters are modifications.)
Whenever a modified creature you control deals combat damage to a player, search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Aven Courier

Flying
Whenever this creature attacks, choose a counter on a permanent you control. Put a counter of that kind on target permanent you control if it doesn't have a counter of that kind on it.