Plague Myr

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
{T}: Add {C}.

Hovermyr

Ichorclaw Myr

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
Whenever Ichorclaw Myr becomes blocked, it gets +2/+2 until end of turn.

Myr Battlesphere

When Myr Battlesphere enters, create four 1/1 colorless Myr artifact creature tokens.
Whenever Myr Battlesphere attacks, you may tap X untapped Myr you control. If you do, Myr Battlesphere gets +X/+0 until end of turn and deals X damage to the player or planeswalker it's attacking.

Urtet, Remnant of Memnarch

Whenever you cast a Myr spell, create a 1/1 colorless Myr artifact creature token.
At the beginning of combat on your turn, untap each Myr you control.
{W}{U}{B}{R}{G}, {T}: Put three +1/+1 counters on each Myr you control. Activate only during your turn.

Myr Scrapling

Sacrifice Myr Scrapling: Put a +1/+1 counter on target creature.

Gold Myr

Have

Dimir Signet

Myr Custodian

When Myr Custodian enters, scry 2. Then each opponent may scry 1. (To scry X, a player looks at the top X cards of their library, then puts any number of them on the bottom and the rest on top in any order.)

Myr Propagator

{3}, {T}: Create a token that's a copy of Myr Propagator.

Myr Quadropod

{3}: Switch Myr Quadropod's power and toughness until end of turn.

Parcel Myr

Silver Myr

Boros Signet

Perilous Myr

When Perilous Myr dies, it deals 2 damage to any target.

Selesnya Signet

Knighted Myr

{2}{W}: Adapt 1. (If this creature has no +1/+1 counters on it, put a +1/+1 counter on it.)
Whenever one or more +1/+1 counters are put on Knighted Myr, it gains double strike until end of turn.

Golgari Signet

Myr Enforcer

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)

Ornithopter of Paradise

Myr Kinsmith

When Myr Kinsmith enters, you may search your library for a Myr card, reveal it, put it into your hand, then shuffle.

Copper Myr

Iron Myr

Gruul Signet

Orzhov Signet

Sol Ring

Rakdos Signet

Palladium Myr

Sarcomite Myr

{2}: Sarcomite Myr gains flying until end of turn.
{2}, Sacrifice Sarcomite Myr: Draw a card.

Alloy Myr

Leaden Myr

Izzet Signet

Myr Prototype

At the beginning of your upkeep, put a +1/+1 counter on Myr Prototype.
Myr Prototype can't attack or block unless you pay {1} for each +1/+1 counter on it.

Azorius Signet

Simic Signet

Suntouched Myr

Sunburst (This enters with a +1/+1 counter on it for each color of mana spent to cast it.)

Myr Convert

Toxic 1 (Players dealt combat damage by this creature also get a poison counter.)
{T}, Pay 2 life: Add one mana of any color.

Myr Sire

When Myr Sire dies, create a 1/1 colorless Phyrexian Myr artifact creature token.

Myr Galvanizer

Other Myr creatures you control get +1/+1.
{1}, {T}: Untap each other Myr you control.