Bite Down on Crime

As an additional cost to cast this spell, you may collect evidence 6. This spell costs {2} less to cast if evidence was collected. (To collect evidence 6, exile cards with total mana value 6 or greater from your graveyard.)
Target creature you control gets +2/+0 until end of turn. It deals damage equal to its power to target creature you don't control.

Call a Surprise Witness

Return target creature card with mana value 3 or less from your graveyard to the battlefield. Put a flying counter on it. It's a Spirit in addition to its other types.

A Killer Among Us

When A Killer Among Us enters, create a 1/1 white Human creature token, a 1/1 blue Merfolk creature token, and a 1/1 red Goblin creature token. Then secretly choose Human, Merfolk, or Goblin.
Sacrifice A Killer Among Us, Reveal the creature type you chose: If target attacking creature token is the chosen type, put three +1/+1 counters on it and it gains deathtouch until end of turn.

Due Diligence

Enchant creature
When Due Diligence enters, target creature you control other than enchanted creature gets +2/+2 and gains vigilance until end of turn.
Enchanted creature gets +2/+2 and has vigilance.

Seasoned Consultant

Whenever you attack with three or more creatures, Seasoned Consultant gets +2/+0 until end of turn.

Crowd-Control Warden

As Crowd-Control Warden enters or is turned face up, put X +1/+1 counters on it, where X is the number of other creatures you control.
Disguise {3}{G/W}{G/W} (You may cast this card face down for {3} as a 2/2 creature with ward {2}. Turn it face up any time for its disguise cost.)

Neighborhood Guardian

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

Airtight Alibi

Flash
Enchant creature
When Airtight Alibi enters, untap enchanted creature. It gains hexproof until end of turn. If it's suspected, it's no longer suspected.
Enchanted creature gets +2/+2 and can't become suspected.

Make Your Move

Destroy target artifact, enchantment, or creature with power 4 or greater.

They Went This Way

Search your library for a basic land card, put it onto the battlefield tapped, then shuffle. Investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")

Griffnaut Tracker

Flying
When Griffnaut Tracker enters, exile up to two target cards from a single graveyard.

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.

Swamp

Forest

Kaya, Spirits' Justice

Whenever one or more creatures you control and/or creature cards in your graveyard are put into exile, you may choose a creature card from among them. Until end of turn, target token you control becomes a copy of it, except it has flying.
+2: Surveil 2, then exile a card from a graveyard.
+1: Create a 1/1 white and black Spirit creature token with flying.
−2: Exile target creature you control. For each other player, exile up to one target creature that player controls.

Not on My Watch

Nervous Gardener

Disguise {G} (You may cast this card face down for {3} as a 2/2 creature with ward {2}. Turn it face up any time for its disguise cost.)
When Nervous Gardener is turned face up, search your library for a land card with a basic land type, reveal it, put it into your hand, then shuffle.

Wispdrinker Vampire

Flying
Whenever another creature you control with power 2 or less enters, each opponent loses 1 life and you gain 1 life.
{5}{W}{B}: Creatures you control with power 2 or less gain deathtouch and lifelink until end of turn.

Defenestrated Phantom

Flying
Disguise {4}{W} (You may cast this card face down for {3} as a 2/2 creature with ward {2}. Turn it face up any time for its disguise cost.)

Plains

Forum Familiar

Disguise {1}{W} (You may cast this card face down for {3} as a 2/2 creature with ward {2}. Turn it face up any time for its disguise cost.)
When Forum Familiar is turned face up, return another target permanent you control to its owner's hand and put a +1/+1 counter on Forum Familiar.

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."