The Signpost Uncommon Game

[Ginuqu]

Slabfiller 1ub
Artifact
xx, : Mill 2, then you may put X target cards from your graveyard on the bottom of your library in any order.
As long as there are at least four creature cards in your graveyard, Slabfiller is a 2/2 Zombie creature.

Next: gr two power matters

[Pygyzy]

Balduvian Wardrummer 1RG
Creature — Human Shaman (U)
Creatures you control with power 2 or less can't be blocked by creatures with toughness 3 or greater.
2/3

Next: UB Rogues

[Ulka]

Cutthroat Cutpurse 2UB
Creature - Human Rogue (U)
Menace
When Cutthroat Cutpurse deals combat damage to a player, that player mills two cards.
Whenever another Rogue enters the battlefield, you may look at the top card of each opponent's library.

Next: WR +1/+1 counters Matter

[lookingupanddown]

Martial Prowess 3RW
Enchantment
At the beginning of your upkeep, you may pay RW. If you do, put a +1/+1 counter on target creature.
2, Remove a +1/+1 counter on target creature you control: That creature gets double strike until end of turn. Activate this ability only any time you could cast a sorcery and only once each turn.
"It was never luck that pushed us forward. It was skill, and the heart to do what's right."
—Kytheon Iora

Next: GU enchantment for sea monster tribal (Kraken, Leviathan, Octopus, and Serpent tribal)

[Pygyzy]

Deep Sea Dive 3UG
Enchantment (U)
Landfall — Reveal the top card of your library. If it's a land card, put it into your hand. If it's a Kraken, Leviathan, Octopus, or Serpent card, put that card onto the battlefield.

Next: WR defenders

[JovialJovian]

Palisade Overseer RW
Creature - Human Soldier
Defender
Whenever a creature you control with defender blocks an attacking creature, the blocking creature assigns combat damage equal to its toughness to the attacking creature, excess damage is dealt to the attacking creature's controlller.
0/3

Next:
RW Vampires

[lookingupanddown]

Blood Fast 1RW
Enchantment - Aura
Enchant Vampire
Enchanted creature can't attack.
At the beginning of your upkeep, put a +1/+1 counter on enchanted creature.
2, Sacrifice Blood Fast: Enchanted creature gets double strike and menace until end of turn. You gain 3 life.

Next: BG creature for deathtouch tribal

[Mookie]

Toxic Amalgam 2BG
Creature - Scorpion Snake
Deathtouch
Whenever a creature you control with deathtouch deals combat damage to a player, that player loses 2 life and you gain 2 life.
2/5

Next: WU enchantment for 'colorless matters'

[JovialJovian]

Subspace Field 1WU
Enchantment
Colorless permanents you control have hexproof.
Colorless spells you cast cost 1 less to cast.

Next:
BR Mutate

[Ulka]

Sadistic Symbiote BR
Creature - Insect Horror
Mutate BR
Sadistic Symbiote can only mutate under creatures you don't control.
Whenever a creature mutates, put a -1/-1 counter on this creature and you discard a card.
0/1

NEXT: UR +1/+1 Counters

Semirelated but not a signal card that I've had the idea for for ages:

Chestburster 3BR
Creature - Horror (U)
Menace
When Chestburster enters the battlefield, mutate it under a creature with 2 time counters on it.
When this creature has no time counters on it, destroy all creatures mutated on top of Chestburster. It's owner gains control of it.
2/2

[Incredium]

Abjuration Savant 3ur
Creature - Human Wizard

The first instant or sorcery spell you cast each turn costs x less to cast, where X is the number of +1/+1 counters on creatures you control.

Warding ur (pay ur, exile this card from your graveyard, put a +1/+1 counter on target wizard you control. Activate this ability only any time you could cast a sorcery.)

0/5

Next: bg enchantment for aristocrats

[lookingupanddown]

Feed the Earth 2BG
Enchantment
Whenever a creature you control dies, you may pay 2. If you do, draw a card and you gain 2 life.
Planting the seeds of life begins from planting the seeds of death.

Next: WB creature for +1/+1 counters

[OneAndOnly]

Kryczni Suckthroat -- WB
Creature - Vampire Rogue
Kryczni Suckthroat enters the battlefield with a +1/+1 counter if you gained life this turn, and a +1/+1 counter if an opponent lost life this turn.
2/2
.
Next: RB enchantment for "sacrifice a land" abilities

[JovialJovian]

Burning Tarpits 3BR
Enchantment
Whenever a land you control is put into a graveyard from the battlefield, target opponent loses life equal to the number of land cards in your graveyard.

Next: Can I request three colors? I'm going to. If you don't like it, pick any two of them. GWB spellslinger.

[Incredium]

Myconid Battlemage wbg
Creature - Fungus Wizard

Vigilance

Whenever you cast an instant or sorcery spell, create a 1/1 green saproling creature token.

2/2

Next: bu for offensive mill

[lookingupanddown]

Bloodthirsty Lobotomist 4UB
Creature - Vampire Wizard
Flying
When Bloodthirsty Lobotomist attacks, it gets +X/+0 until end of turn, where X is the number of creature cards in defending player's graveyard.
Whenever Bloodthirsty Lobotomist deals combat damage to a player, that player mills three cards.
3/3

Next: WU creature for blink

[Mookie]

Visiting Phantasm 1WU
Creature - Spirit
Flying
: exile Visiting Phantasm and another target creature you control. Return both to the battlefield at the beginning of the next end step.
1/3

Next: BR artifact for 'three of a kind' matters

[JovialJovian]

Kinsblood Medallion 2
Artifact
Creature spells you cast cost 1 less to cast for each creature you control with the same name as that spell.
BR, Sacrifice Kinsblood Medallion and three nontoken creatures with the same name: Kinsblood Medallion deals 9 damage to any target.

Next: GU Gorgons

[Mookie]

Stonewater Gorgon 2GU
Creature - Elemental Gorgon
Whenever a creature an opponent controls blocks or is blocked by a Gorgon you control, tap that creature. It doesn't untap for as long as you control Stonewater Gorgon.
UG: target creature blocks a Gorgon this turn if able.
2/5

Next: WG enchantment for wolf/werewolf tribal

[lookingupanddown]

Silverfur Vigil 2GW
Enchantment
Wolves and Werewolves you control have vigilance.
2GG: Create a 2/2 green Wolf Warrior creature token.
"We are the last of the wolfir. We cannot afford to turn down those called to our watch."
—Pavel, Silverfur alpha

Next: RG sorcery for power 4 or greater matters

[void_nothing]

Fires of the Frontier RG
Sorcery
Creatures you control get +1/+1 and gain trample and haste until end of turn.
Ferocious - Draw a card if you control a creature with power 4 or greater.

Next: RW creature for modal matters

[JovialJovian]

Khenra Sandspinner 1RW
Creature - Jackal Shaman
Whenever you choose modes for a spell or ability, choose an additional mode at random. The additional mode may be the same as a chosen mode.
3/2

Next: UB instant for tribal wizards

[lookingupanddown]

Arcane Retrieval (u/b)(u/b)(u/b)(u/b)
Instant
Search your library and graveyard for a card with converted mana cost X or less, where X is the number of Wizards you control, then put it into your hand.

Next: WB sorcery for Rebel tribal

[JovialJovian]

Call the Cohort 4WB
Sorcery
This spell costs 2 less to cast and may be cast as though it has flash if a Rebel died this turn.
Search your library for a Rebel creature card with converted mana cost less than or equal to the converted mana cost of target creature you control, put that card onto the battlefield, then shuffle your library.

Next: GU artifact for Clues

[void_nothing]

Barkbound Journal GU
Artifact - Clue
Whenever Barkbound Journal or another artifact is put into your graveyard from the battlefield, look at the top card of target player's library. You may exile that card. If you don't, create a 0/2 green Plant Wall creature token with defender and reach.
2, Sacrifice Barkbound Journal: Draw a card.

Next: UB fliers matter