Catacomb Dragon

Flying
Whenever Catacomb Dragon becomes blocked by a nonartifact, non-Dragon creature, that creature gets -X/-0 until end of turn, where X is half the creature's power, rounded down.

Plains

Nicol Bolas, Dragon-God

Nicol Bolas, Dragon-God has all loyalty abilities of all other planeswalkers on the battlefield.
+1: You draw a card. Each opponent exiles a card from their hand or a permanent they control.
−3: Destroy target creature or planeswalker.
−8: Each opponent who doesn't control a legendary creature or planeswalker loses the game.

Cloud Dragon

Flying
Cloud Dragon can block only creatures with flying.

Staff of the Wild Magus

Whenever you cast a green spell or a Forest you control enters, you gain 1 life.

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.

Dragon Breath

Enchant creature
Enchanted creature has haste.
{R}: Enchanted creature gets +1/+0 until end of turn.
When a creature with mana value 6 or greater enters, you may return Dragon Breath from your graveyard to the battlefield attached to that creature.

Temple of the Dragon Queen

As Temple of the Dragon Queen enters, you may reveal a Dragon card from your hand. Temple of the Dragon Queen enters tapped unless you revealed a Dragon card this way or you control a Dragon.
As Temple of the Dragon Queen enters, choose a color.
{T}: Add one mana of the chosen color.

Ebon Dragon

Flying
When Ebon Dragon enters, you may have target opponent discard a card.

Canopy Dragon

Trample
{1}{G}: Canopy Dragon gains flying and loses trample until end of turn.

Dragon Mask

{3}, {T}: Target creature you control gets +2/+2 until end of turn. Return it to its owner's hand at the beginning of the next end step. (Return it only if it's on the battlefield.)

Mountain

Dragon Blood

{3}, {T}: Put a +1/+1 counter on target creature.

Dragon Appeasement

Skip your draw step.
Whenever you sacrifice a creature, you may draw a card.

Nicol Bolas, God-Pharaoh

+2: Target opponent exiles cards from the top of their library until they exile a nonland card. Until end of turn, you may cast that card without paying its mana cost.
+1: Each opponent exiles two cards from their hand.
−4: Nicol Bolas, God-Pharaoh deals 7 damage to target opponent, creature an opponent controls, or planeswalker an opponent controls.
−12: Exile each nonland permanent your opponents control.

Ramos, Dragon Engine

Flying
Whenever you cast a spell, put a +1/+1 counter on Ramos for each of that spell's colors.
Remove five +1/+1 counters from Ramos: Add {W}{W}{U}{U}{B}{B}{R}{R}{G}{G}. Activate only once each turn.

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.)

Covetous Dragon

Flying
When you control no artifacts, sacrifice Covetous Dragon.

Dragon Arch

{2}, {T}: You may put a multicolored creature card from your hand onto the battlefield.

Red Dragon

Flying
Fire Breath — When Red Dragon enters, it deals 4 damage to each opponent.

Forest

Creature Bond

Enchant creature
When enchanted creature dies, Creature Bond deals damage equal to that creature's toughness to the creature's controller.

Staff of the Mind Magus

Whenever you cast a blue spell or an Island you control enters, you gain 1 life.

Dragon Engine

{2}: Dragon Engine gets +1/+0 until end of turn.

Staff of the Death Magus

Whenever you cast a black spell or a Swamp you control enters, you gain 1 life.

Bone Dragon

Flying
{3}{B}{B}, Exile seven other cards from your graveyard: Return Bone Dragon from your graveyard to the battlefield tapped.

Acolyte of Bahamut

Commander creatures you own have "The first Dragon spell you cast each turn costs {2} less to cast."

Dragon Egg

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

Swamp

Staff of the Flame Magus

Whenever you cast a red spell or a Mountain you control enters, you gain 1 life.

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.

Dragon Fangs

Enchant creature
Enchanted creature gets +1/+1 and has trample.
When a creature with mana value 6 or greater enters, you may return Dragon Fangs from your graveyard to the battlefield attached to that creature.

Staff of the Sun Magus

Whenever you cast a white spell or a Plains you control enters, you gain 1 life.

Stormbreath Dragon

Flying, haste, protection from white
{5}{R}{R}: Monstrosity 3. (If this creature isn't monstrous, put three +1/+1 counters on it and it becomes monstrous.)
When Stormbreath Dragon becomes monstrous, it deals damage to each opponent equal to the number of cards in that player's hand.

Dragon Turtle

Flash
Drag Below — When Dragon Turtle enters, tap it and up to one target creature an opponent controls. They don't untap during their controllers' next untap steps.

Stoneforge Masterwork

Equipped creature gets +1/+1 for each other creature you control that shares a creature type with it.
Equip {2}

Fountain of Renewal

At the beginning of your upkeep, you gain 1 life.
{3}, Sacrifice Fountain of Renewal: Draw a card.

Dragon Grip

Ferocious — If you control a creature with power 4 or greater, you may cast Dragon Grip as though it had flash. (You may cast it any time you could cast an instant.)
Enchant creature
Enchanted creature gets +2/+0 and has first strike.

Dragon Bell Monk

Vigilance
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)

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.)

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."

Dragon Fodder

Create two 1/1 red Goblin creature tokens.

Dragon Mage

Flying
Whenever this creature deals combat damage to a player, each player discards their hand, then draws seven cards.

Dragon Scales

Enchant creature
Enchanted creature gets +1/+2 and has vigilance.
When a creature with mana value 6 or greater enters, you may return Dragon Scales from your graveyard to the battlefield attached to that creature.