Mind Rot

Dismal Backwater

Dismal Backwater enters tapped.
When Dismal Backwater enters, you gain 1 life.
{T}: Add {U} or {B}.

Swamp

Commander's Sphere

{T}: Add one mana of any color in your commander's color identity.
Sacrifice Commander's Sphere: Draw a card.

Ruthless Deathfang

Flying
Whenever you sacrifice a creature, target opponent sacrifices a creature.

Renari, Merchant of Marvels

You may cast Dragon spells and artifact spells as though they had flash.
Choose a Background (You can have a Background as a second commander.)

Dimir Cluestone

{T}: Add {U} or {B}.
{U}{B}, {T}, Sacrifice Dimir Cluestone: Draw a card.

Entropic Cloud

Creatures you control gain deathtouch until end of turn. (Then exile this card. You may cast the creature later from exile.)

Topaz Dragon

Topaz Dragon // Entropic Cloud

Sand Augury

Scry 1, then draw a card. (Then exile this card. You may cast the creature later from exile.)

Young Blue Dragon

Young Blue Dragon // Sand Augury

Blue Dragon

Flying
Lightning Breath — When Blue Dragon enters, until your next turn, target creature an opponent controls gets -3/-0, up to one other target creature gets -2/-0, and up to one other target creature gets -1/-0.

Dimir Guildgate

Dimir Guildgate enters tapped.
{T}: Add {U} or {B}.

Island

Tormented Thoughts

As an additional cost to cast this spell, sacrifice a creature.
Target player discards a number of cards equal to the sacrificed creature's power.

Warden of Evos Isle

Flying
Creature spells with flying you cast cost {1} less to cast.

Nimbleclaw Adept

Bigby's Hand — {T}: Untap two other target permanents. Activate only as a sorcery and only once each turn.

Scourge of Nel Toth

Flying
You may cast Scourge of Nel Toth from your graveyard by paying {B}{B} and sacrificing two creatures rather than paying its mana cost.

Silumgar, the Drifting Death

Flying, hexproof
Whenever a Dragon you control attacks, creatures defending player controls get -1/-1 until end of turn.

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Ancient Craving

You draw three cards and you lose 3 life.

Read the Bones

Scry 2, then draw two cards. You lose 2 life. (To scry 2, look at the top two cards of your library, then put any number of them on the bottom and the rest on top in any order.)

Run Away Together

Choose two target creatures controlled by different players. Return those creatures to their owners' hands.

Sign in Blood

Target player draws two cards and loses 2 life.

Dragonborn Looter

{1}, {T}: Draw a card, then discard a card.

Keiga, the Tide Star

Flying
When Keiga, the Tide Star dies, gain control of target creature.

Noxious Dragon

Flying
When Noxious Dragon dies, you may destroy target creature with mana value 3 or less.

Feed the Swarm

Destroy target creature or enchantment an opponent controls. You lose life equal to that permanent's mana value.

Psionic Pulse

Counter target noncreature spell. (Then exile this card. You may cast the creature later from exile.)

Sapphire Dragon

Flying
Whenever Sapphire Dragon attacks or blocks, scry 2.

Sapphire Dragon // Psionic Pulse

Deadly Dispute

As an additional cost to cast this spell, sacrifice an artifact or creature.
Draw two cards and create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Charcoal Diamond

Charcoal Diamond enters tapped.
{T}: Add {B}.

Acid-Spewer Dragon

Flying, deathtouch
Megamorph {5}{B}{B} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its megamorph cost and put a +1/+1 counter on it.)
When Acid-Spewer Dragon is turned face up, put a +1/+1 counter on each other Dragon creature you control.

Propaganda

Creatures can't attack you unless their controller pays {2} for each creature they control that's attacking you.

Foul-Tongue Invocation

As an additional cost to cast this spell, you may reveal a Dragon card from your hand.
Target player sacrifices a creature. If you revealed a Dragon card or controlled a Dragon as you cast this spell, you gain 4 life.

Murder

Sky Diamond

Pirate's Prize

Draw two cards. Create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Draconic Lore

This spell costs {2} less to cast if you control a Dragon.
Draw three cards.

Thriving Moor

Thriving Moor enters tapped. As it enters, choose a color other than black.
{T}: Add {B} or one mana of the chosen color.

Pseudodragon Familiar

Flying
{2}{U}: Target creature gains flying until end of turn.

Duress

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

Capsizing Wave

Return target creature to its owner's hand. (Then exile this card. You may cast the creature later from exile.)

Sword Coast Serpent

Sword Coast Serpent can't be blocked as long as you've cast a noncreature spell this turn.

Sword Coast Serpent // Capsizing Wave

Thriving Isle

Thriving Isle enters tapped. As it enters, choose a color other than blue.
{T}: Add {U} or one mana of the chosen color.

Dream Fracture

Counter target spell. Its controller draws a card.
Draw a card.

Sivitri, Dragon Master

+1: Until your next turn, creatures can't attack you or planeswalkers you control unless their controller pays 2 life for each of those creatures.
−3: Search your library for a Dragon card, reveal it, put it into your hand, then shuffle.
−7: Destroy all non-Dragon creatures.
Sivitri, Dragon Master can be your commander.