Mainboard Switcher

Mind Rot

Rain of Daggers

Destroy all creatures target opponent controls. You lose 2 life for each creature destroyed this way.

Lab Rats

Buyback {4} (You may pay an additional {4} as you cast this spell. If you do, put this card into your hand as it resolves.)
Create a 1/1 black Rat creature token.

Crypt Rats

{X}: Crypt Rats deals X damage to each creature and each player. Spend only black mana on X.

Hand of Death

Sideboard

Virtue's Ruin

Dread Charge

Black creatures you control can't be blocked this turn except by black creatures.

Foul Imp

Flying
When Foul Imp enters, you lose 2 life.

Nature's Ruin

Bad Moon

Ancient Craving

You draw three cards and you lose 3 life.

Pestilence Rats

Pestilence Rats's power is equal to the number of other Rats on the battlefield. (For example, as long as there are two other Rats on the battlefield, Pestilence Rats's power and toughness are 2/3.)

Assassin's Blade

Cast this spell only during the declare attackers step and only if you've been attacked this step.
Destroy target nonblack attacking creature.

Swamp

Cruel Edict

Target opponent sacrifices a creature of their choice.

Sewer Rats

{B}, Pay 1 life: Sewer Rats gets +1/+0 until end of turn. Activate no more than three times each turn.

Razortooth Rats

Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)

Ravenous Rats

When Ravenous Rats enters, target opponent discards a card.

Dry Spell

Dry Spell deals 1 damage to each creature and each player.

Swarm of Rats

Swarm of Rats's power is equal to the number of Rats you control.