Nightmare

Flying (This creature can't be blocked except by creatures with flying or reach.)
Nightmare's power and toughness are each equal to the number of Swamps you control.

Vampire of the Dire Moon

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)
Lifelink (Damage dealt by this creature also causes you to gain that much life.)

Murder

Defile

Target creature gets -1/-1 until end of turn for each Swamp you control.

Sign in Blood

Target player draws two cards and loses 2 life.

Morbid Opportunist

Whenever one or more other creatures die, draw a card. This ability triggers only once each turn.

Burglar Rat

When this creature enters, each opponent discards a card.

Plasmancer

Flying
Dynastic Advisor — When Plasmancer enters, search your library for a basic Swamp card, reveal it, put it into your hand, then shuffle.

Phyrexian Rager

When Phyrexian Rager enters, you draw a card and you lose 1 life.

Duress

Target opponent reveals their hand. You choose a noncreature, nonland card from it. That player discards that card.

Swamp

Boot Nipper

Boot Nipper enters with your choice of a deathtouch counter or a lifelink counter on it.

Locthwain Paladin

Menace (This creature can't be blocked except by two or more creatures.)
Adamant — If at least three black mana was spent to cast this spell, Locthwain Paladin enters with a +1/+1 counter on it.

Indulgent Tormentor

Flying
At the beginning of your upkeep, draw a card unless target opponent sacrifices a creature of their choice or pays 3 life.