Case of the Pilfered Proof

Whenever a Detective you control enters or is turned face up, put a +1/+1 counter on it.
To solve — You control three or more Detectives. (If unsolved, solve at the beginning of your end step.)
Solved — If one or more tokens would be created under your control, those tokens plus a Clue token are created instead. (It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")

Toxin Analysis

Target creature gains deathtouch and lifelink until end of turn. Investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")

Insidious Roots

Creature tokens you control have "{T}: Add one mana of any color."
Whenever one or more creature cards leave your graveyard, create a 0/1 green Plant creature token, then put a +1/+1 counter on each Plant you control.

Plains

Curious Inquiry

Enchant creature
Enchanted creature gets +1/+1 and has "Whenever this creature deals combat damage to a player, investigate." (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")

Krovod Haunch

Equipped creature gets +2/+0.
{2}, {T}, Sacrifice Krovod Haunch: You gain 3 life.
When Krovod Haunch is put into a graveyard from the battlefield, you may pay {1}{W}. If you do, create two 1/1 white Dog creature tokens.
Equip {2}

Culvert Ambusher

When Culvert Ambusher enters or is turned face up, target creature blocks this turn if able.
Disguise {4}{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.)

Dramatic Accusation

Enchant creature
When Dramatic Accusation enters, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.
{U}{U}: Shuffle enchanted creature into its owner's library.

Forensic Gadgeteer

Whenever you cast an artifact spell, investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")
Activated abilities of artifacts you control cost {1} less to activate. This effect can't reduce the mana in that cost to less than one mana.

Case of the Filched Falcon

When this Case enters, investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")
To solve — You control three or more artifacts. (If unsolved, solve at the beginning of your end step.)
Solved — {2}{U}, Sacrifice this Case: Put four +1/+1 counters on target noncreature artifact. It becomes a 0/0 Bird creature with flying in addition to its other types.

Urgent Necropsy

As an additional cost to cast this spell, collect evidence X, where X is the total mana value of the permanents this spell targets.
Destroy up to one target artifact, up to one target creature, up to one target enchantment, and up to one target planeswalker.

Illicit Masquerade

Flash
When Illicit Masquerade enters, put an impostor counter on each creature you control.
Whenever a creature you control with an impostor counter on it dies, exile it. Return up to one other target creature card from your graveyard to the battlefield.

Ezrim, Agency Chief

Flying
When Ezrim, Agency Chief enters, investigate twice. (To investigate, create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")
{1}, Sacrifice an artifact: Ezrim gains your choice of vigilance, lifelink, or hexproof until end of turn.

Behind the Mask

As an additional cost to cast this spell, you may collect evidence 6. (Exile cards with total mana value 6 or greater from your graveyard.)
Until end of turn, target artifact or creature becomes an artifact creature with base power and toughness 4/3. If evidence was collected, it has base power and toughness 1/1 until end of turn instead.

Marketwatch Phantom

Whenever another creature you control with power 2 or less enters, Marketwatch Phantom gains flying until end of turn.

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.")

Niv-Mizzet, Guildpact

Flying, hexproof from multicolored
Whenever Niv-Mizzet, Guildpact deals combat damage to a player, it deals X damage to any target, target player draws X cards, and you gain X life, where X is the number of different color pairs among permanents you control that are exactly two colors.

Private Eye

Other Detectives you control get +1/+1.
Whenever you draw your second card each turn, target Detective can't be blocked this turn.

Cold Case Cracker

Flying
When Cold Case Cracker dies, investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")

The Pride of Hull Clade

This spell costs {X} less to cast, where X is the total toughness of creatures you control.
Defender
{2}{U}{U}: Until end of turn, target creature you control gets +1/+0, gains "Whenever this creature deals combat damage to a player, draw cards equal to its toughness," and can attack as though it didn't have defender.

Forest

Loxodon Eavesdropper

When Loxodon Eavesdropper enters, investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")
Whenever you draw your second card each turn, Loxodon Eavesdropper gets +1/+1 and gains vigilance until end of turn.

Island

Eliminate the Impossible

Investigate. Creatures your opponents control get -2/-0 until end of turn. If any of them are suspected, they're no longer suspected. (To investigate, create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")

Benthic Criminologists

Whenever Benthic Criminologists enters or attacks, you may sacrifice an artifact. If you do, draw a card.

Jaded Analyst

Defender
Whenever you draw your second card each turn, Jaded Analyst loses defender and gains vigilance until end of turn.

Projektor Inspector

Whenever Projektor Inspector or another Detective you control enters and whenever a Detective you control is turned face up, you may draw a card. If you do, discard a card.

Reasonable Doubt

Counter target spell unless its controller pays {2}.
Suspect up to one target creature. (A suspected creature has menace and can't block.)