Plains

Novice Inspector

When Novice Inspector enters, investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")

Serra Faithkeeper

Invasion of Dominaria

(As a Siege enters, choose an opponent to protect it. You and others can attack it. When it's defeated, exile it, then cast it transformed.)
When Invasion of Dominaria enters, you gain 4 life and draw a card.

Invasion of Dominaria // Serra Faithkeeper

Cosmium Blast

Cosmium Blast deals 4 damage to target attacking or blocking creature.

Acrobatic Leap

Target creature gets +1/+3 and gains flying until end of turn. Untap it.

Detective

Kill Shot

Ruin-Lurker Bat

Flying, lifelink
At the beginning of your end step, if you descended this turn, scry 1. (You descended if a permanent card was put into your graveyard from anywhere.)

Inside Source

When Inside Source enters, create a 2/2 white and blue Detective creature token.
{3}, {T}: Target Detective you control gets +2/+0 and gains vigilance until end of turn. Activate only as a sorcery.

On the Job

Creatures you control get +2/+1 until end of turn. Investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")

Clue

{2}, Sacrifice this artifact: Draw a card.

Regal Bunnicorn

Regal Bunnicorn's power and toughness are each equal to the number of nonland permanents you control.

Neighborhood Guardian

Whenever another creature you control with power 2 or less enters, target creature you control gets +1/+1 until end of turn.

Tenth District Hero

{1}{W}, Collect evidence 2: Tenth District Hero becomes a Human Detective with base power and toughness 4/4 and gains vigilance.
{2}{W}, Collect evidence 4: If Tenth District Hero is a Detective, it becomes a legendary creature named Mileva, the Stalwart, it has base power and toughness 5/5, and it gains "Other creatures you control have indestructible."

Petrify

Enchant artifact or creature
Enchanted permanent can't attack or block, and its activated abilities can't be activated.

Case of the Gateway Express

When this Case enters, choose target creature you don't control. Each creature you control deals 1 damage to that creature.
To solve — Three or more creatures attacked this turn. (If unsolved, solve at the beginning of your end step.)
Solved — Creatures you control get +1/+0.

Union of the Third Path

Draw a card, then you gain life equal to the number of cards in your hand.

Sanguine Evangelist

Battle cry (Whenever this creature attacks, each other attacking creature gets +1/+0 until end of turn.)
When Sanguine Evangelist enters or dies, create a 1/1 black Bat creature token with flying.

Ironpaw Aspirant

When Ironpaw Aspirant enters, put a +1/+1 counter on target creature.

Miner's Guidewing

Flying, vigilance
When Miner's Guidewing dies, target creature you control explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on that creature, then put the card back or put it into your graveyard.)