Phyresis

Enchant creature
Enchanted creature has infect. (It deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

Golgari Signet

Gruul Signet

Atogatog

Sacrifice an Atog creature: Atogatog gets +X/+X until end of turn, where X is the sacrificed creature's power.

Megatog

Sacrifice an artifact: This creature gets +3/+3 and gains trample until end of turn.

Maskwood Nexus

Creatures you control are every creature type. The same is true for creature spells you control and creature cards you own that aren't on the battlefield.
{3}, {T}: Create a 2/2 blue Shapeshifter creature token with changeling. (It is every creature type.)

Ulvenwald Tracker

{1}{G}, {T}: Target creature you control fights another target creature.

Azorius Signet

Karmic Guide

Flying, protection from black
Echo {3}{W}{W} (At the beginning of your upkeep, if this came under your control since the beginning of your last upkeep, sacrifice it unless you pay its echo cost.)
When this creature enters, return target creature card from your graveyard to the battlefield.

Phyrexian Altar

Sacrifice a creature: Add one mana of any color.

Boros Signet

Fellwar Stone

{T}: Add one mana of any color that a land an opponent controls could produce.

Sol Ring

Simic Signet

Orzhov Signet

Reveillark

Flying
When this creature leaves the battlefield, return up to two target creature cards with power 2 or less from your graveyard to the battlefield.
Evoke {5}{W} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

Rakdos Signet

Izzet Signet

Arcane Signet

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

Dimir Signet

Grafted Exoskeleton

Equipped creature gets +2/+2 and has infect. (It deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
Whenever Grafted Exoskeleton becomes unattached from a permanent, sacrifice that permanent.
Equip {2}