Mayhem Patrol

Menace (This creature can't be blocked except by two or more creatures.)
Whenever this creature attacks, target creature gets +1/+0 until end of turn.
Blitz {1}{R} (If you cast this spell for its blitz cost, it gains haste and "When this creature dies, draw a card." Sacrifice it at the beginning of the next end step.)

Swamp

Balduvian Atrocity

Kicker {R} (You may pay an additional {R} as you cast this spell.)
Menace
When this creature enters, if it was kicked, return target creature card with mana value 3 or less from your graveyard to the battlefield. It gains haste. Sacrifice it at the beginning of the next end step.

Burn Bright

Creatures you control get +2/+0 until end of turn.

Purphoros's Emissary

Bestow {6}{R} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached.)
Menace (This creature can't be blocked except by two or more creatures.)
Enchanted creature gets +3/+3 and has menace.

Gluttonous Slug

Menace
Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)

Loathsome Curator

Exploit (When this creature enters, you may sacrifice a creature.)
Menace
When this creature exploits a creature, destroy target creature you don't control with mana value 3 or less.

Rakdos Trumpeter

Menace (This creature can't be blocked except by two or more creatures.)
{3}{R}: This creature gets +2/+0 until end of turn.

Tramway Station

This land enters tapped.
{T}: Add {B} or {R}.
{2}{B}{R}, {T}, Sacrifice this land: Draw a card.

Flowstone Kavu

Menace (This creature can't be blocked except by two or more creatures.)
{R}: This creature gets +1/-1 until end of turn.

Mountain

Strangling Soot

Destroy target creature with toughness 3 or less.
Flashback {5}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Tentative Connection

This spell costs {3} less to cast if you control a creature with menace.
Gain control of target creature until end of turn. Untap that creature. It gains haste until end of turn.

Frillscare Mentor

When this creature enters, put a menace counter on target non-Human creature you control. (It can't be blocked except by two or more creatures.)
{2}{R}, {T}: Put a +1/+1 counter on each creature you control with menace.