Presumed Dead

Until end of turn, target creature gets +2/+0 and gains "When this creature dies, return it to the battlefield under its owner's control and suspect it." (A suspected creature has menace and can't block.)

A Killer Among Us

When this enchantment 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 this enchantment, 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.

Nelly Borca, Impulsive Accuser

Vigilance
Whenever Nelly Borca attacks, suspect target creature. Then goad all suspected creatures. (A suspected creature has menace and can't block.)
Whenever one or more creatures an opponent controls deal combat damage to one or more of your opponents, you and the controller of those creatures each draw a card.

Witness Protection

Enchant creature
Enchanted creature loses all abilities and is a green and white Citizen creature with base power and toughness 1/1 named Legitimate Businessperson. (It loses all other colors, card types, creature types, and names.)

The Most Dangerous Gamer

Deathtouch
Whenever The Most Dangerous Gamer enters or attacks, open an Attraction.
Whenever you open an Attraction, put a +1/+1 counter on The Most Dangerous Gamer.
Whenever you claim the prize of an Attraction, destroy target permanent.

Murder

Crawlspace

No more than two creatures can attack you each combat.

Game Over

This spell costs {2} less to cast if a player's life total is less than or equal to half their starting life total.
Destroy all creatures.

Repeat Offender

{2}{B}: If this creature is suspected, put a +1/+1 counter on it. Otherwise, suspect it. (A suspected creature has menace and can't block.)

Case of the Stashed Skeleton

When this Case enters, create a 2/1 black Skeleton creature token and suspect it. (It has menace and can't block.)
To solve — You control no suspected Skeletons. (If unsolved, solve at the beginning of your end step.)
Solved — {1}{B}, Sacrifice this Case: Search your library for a card, put it into your hand, then shuffle. Activate only as a sorcery.

It Doesn't Add Up

Return target creature card from your graveyard to the battlefield. Suspect it. (It has menace and can't block.)