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.

Snow-Covered Forest

Livaan, Cultist of Tiamat

Whenever you cast a noncreature spell, target creature gets +X/+0 until end of turn, where X is that spell's mana value.
Choose a Background (You can have a Background as a second commander.)

Backdraft Hellkite

Flying
Whenever Backdraft Hellkite attacks, each instant and sorcery card in your graveyard gains flashback until end of turn. The flashback cost is equal to its mana cost.

Ancient Silver Dragon

Flying
Whenever Ancient Silver Dragon deals combat damage to a player, roll a d20. Draw cards equal to the result. You have no maximum hand size for the rest of the game.

Breeding Pool

({T}: Add {G} or {U}.)
As Breeding Pool enters, you may pay 2 life. If you don't, it enters tapped.

Hellkite Tyrant

Flying, trample
Whenever Hellkite Tyrant deals combat damage to a player, gain control of all artifacts that player controls.
At the beginning of your upkeep, if you control twenty or more artifacts, you win the game.

Marsh Flats

{T}, Pay 1 life, Sacrifice Marsh Flats: Search your library for a Plains or Swamp card, put it onto the battlefield, then shuffle.

Snow-Covered Plains

Swan Song

Counter target enchantment, instant, or sorcery spell. Its controller creates a 2/2 blue Bird creature token with flying.

Talisman of Curiosity

{T}: Add {C}.
{T}: Add {G} or {U}. Talisman of Curiosity deals 1 damage to you.

Balefire Dragon

Flying
Whenever Balefire Dragon deals combat damage to a player, it deals that much damage to each creature that player controls.

Swamp

Forest

Sol Ring

Chaos Dragon

Flying, haste
Chaos Dragon attacks each combat if able.
At the beginning of combat on your turn, each player rolls a d20. If one or more opponents had the highest result, Chaos Dragon can't attack those players or planeswalkers they control this combat.

Arashin Sovereign

Flying
When Arashin Sovereign dies, you may put it on your choice of the top or bottom of its owner's library.

Tiamat

Flying
When Tiamat enters, if you cast it, search your library for up to five Dragon cards not named Tiamat that each have different names, reveal them, put them into your hand, then shuffle.

Ancient Copper Dragon

Flying
Whenever Ancient Copper Dragon deals combat damage to a player, roll a d20. You create a number of Treasure tokens equal to the result.

Korlessa, Scale Singer

You may look at the top card of your library any time.
You may cast Dragon spells from the top of your library.

Farseek

Search your library for a Plains, Island, Swamp, or Mountain card, put it onto the battlefield tapped, then shuffle.

Godless Shrine

({T}: Add {W} or {B}.)
As Godless Shrine enters, you may pay 2 life. If you don't, it enters tapped.

Snow-Covered Mountain

Island

Ancient Bronze Dragon

Flying
Whenever Ancient Bronze Dragon deals combat damage to a player, roll a d20. When you do, put X +1/+1 counters on each of up to two target creatures, where X is the result.

Hellkite Courser

Flying
When Hellkite Courser enters, you may put a commander you own from the command zone onto the battlefield. It gains haste. Return it to the command zone at the beginning of the next end step.

Bayou

Plateau

Loch Dragon

Flying
Whenever Loch Dragon enters or attacks, you may discard a card. If you do, draw a card.

Talisman of Progress

{T}: Add {C}.
{T}: Add {W} or {U}. Talisman of Progress deals 1 damage to you.

Lozhan, Dragons' Legacy

Flying
Whenever you cast an Adventure or Dragon spell, Lozhan, Dragons' Legacy deals damage equal to that spell's mana value to any target that isn't a commander.

The Ur-Dragon

Eminence — As long as The Ur-Dragon is in the command zone or on the battlefield, other Dragon spells you cast cost {1} less to cast.
Flying
Whenever one or more Dragons you control attack, draw that many cards, then you may put a permanent card from your hand onto the battlefield.

Evolving Wilds

{T}, Sacrifice this land: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Snow-Covered Island

Arcades Sabboth

Flying
At the beginning of your upkeep, sacrifice Arcades Sabboth unless you pay {G}{W}{U}.
Each untapped creature you control gets +0/+2 as long as it's not attacking.
{W}: Arcades Sabboth gets +0/+1 until end of turn.

Ancient Hellkite

Flying
{R}: Ancient Hellkite deals 1 damage to target creature defending player controls. Activate only if Ancient Hellkite is attacking.

Kodama's Reach

Search your library for up to two basic land cards, reveal those cards, put one onto the battlefield tapped and the other into your hand, then shuffle.

Arcane Signet

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

Mountain

Pact of Negation

Counter target spell.
At the beginning of your next upkeep, pay {3}{U}{U}. If you don't, you lose the game.

Atarka, World Render

Flying, trample
Whenever a Dragon you control attacks, it gains double strike until end of turn.

Plains

Exploration

You may play an additional land on each of your turns.

Snow-Covered Swamp

Avaricious Dragon

Flying
At the beginning of your draw step, draw an additional card.
At the beginning of your end step, discard your hand.