Ancient Bronze Dragon

Flying
Whenever this creature 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.

Ambitious Dragonborn

This creature enters with X +1/+1 counters on it, where X is the greatest power among creatures you control and creature cards in your graveyard.

Bhaal's Invoker

Scorching Ray — {8}: This creature deals 4 damage to each opponent.

Ancient Copper Dragon

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

Atarka, World Render

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

Magnetic Mountain

Blue creatures don't untap during their controllers' untap steps.
At the beginning of each player's upkeep, that player may choose any number of tapped blue creatures they control and pay {4} for each creature chosen this way. If the player does, untap those creatures.

Akoum Hellkite

Flying
Landfall — Whenever a land you control enters, this creature deals 1 damage to any target. If that land is a Mountain, this creature deals 2 damage instead.

Dragon Broodmother

Flying
At the beginning of each upkeep, create a 1/1 red and green Dragon creature token with flying and devour 2. (As the token enters, you may sacrifice any number of creatures. It enters with twice that many +1/+1 counters on it.)

Mountain

Skanos Dragonheart

Whenever Skanos Dragonheart attacks, it gets +X/+X until end of turn, where X is the greatest power among other Dragons you control and Dragon cards in your graveyard.
Choose a Background (You can have a Background as a second commander.)

Dragon Hatchling

Flying
{R}: This creature gets +1/+0 until end of turn.

Demanding Dragon

Flying
When this creature enters, it deals 5 damage to target opponent unless that player sacrifices a creature of their choice.

Draconic Muralists

When this creature dies, you may search your library for a Dragon card, reveal it, put it into your hand, then shuffle.

Archwing Dragon

Flying, haste
At the beginning of the end step, return this creature to its owner's hand.

Dragon Egg

Defender
When this creature dies, create a 2/2 red Dragon creature token with flying and "{R}: This token gets +1/+0 until end of turn."

Chaos Dragon

Flying, haste
This creature 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, this creature can't attack those players or planeswalkers they control this combat.

Dragon Cultist

Commander creatures you own have "At the beginning of your end step, if a source you controlled dealt 5 or more damage this turn, create a 4/4 red Dragon creature token with flying."

Ancient Hellkite

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

Madblind Mountain

({T}: Add {R}.)
This land enters tapped.
{R}, {T}: Shuffle your library. Activate only if you control two or more red permanents.

Dragonborn Champion

Trample
Whenever a source you control deals 5 or more damage to a player, draw a card.

Explosive Crystal

Explosive Crystal deals 4 damage divided as you choose among any number of targets. (Then exile this card. You may cast the creature later from exile.)