ramp/cost reducer

Dragonlord's Servant

Dragon spells you cast cost {1} less to cast.

lands

Watery Grave

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

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.)

Treasures

Goldspan Dragon

Flying, haste
Whenever Goldspan Dragon attacks or becomes the target of a spell, create a Treasure token.
Treasures you control have "{T}, Sacrifice this artifact: Add two mana of any one color."

Reflections of Littjara

As Reflections of Littjara enters, choose a creature type.
Whenever you cast a spell of the chosen type, copy that spell. (A copy of a permanent spell becomes a token.)

Expensive Taste

Exile the top two cards of target opponent's library face down. You may look at and play those cards for as long as they remain exiled.

Decadent Dragon

Flying, trample
Whenever Decadent Dragon attacks, create a Treasure token.

Decadent Dragon // Expensive Taste

Sarkhan, Soul Aflame

Dragon spells you cast cost {1} less to cast.
Whenever a Dragon you control enters, you may have Sarkhan, Soul Aflame become a copy of it until end of turn, except its name is Sarkhan, Soul Aflame and it's legendary in addition to its other types.

Bloodstained Mire

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

boardwipe

Crux of Fate

Choose one —
• Destroy all Dragon creatures.
• Destroy all non-Dragon creatures.

Crumbling Necropolis

Crumbling Necropolis enters tapped.
{T}: Add {U}, {B}, or {R}.

Urza's Incubator

As Urza's Incubator enters, choose a creature type.
Creature spells of the chosen type cost {2} less to cast.

Balefire Dragon

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

Sprite Dragon

Flying, haste
Whenever you cast a noncreature spell, put a +1/+1 counter on Sprite Dragon.

extra combat

Relentless Assault

Untap all creatures that attacked this turn. After this main phase, there is an additional combat phase followed by an additional main phase.

removal

Dragon's Fire

As an additional cost to cast this spell, you may reveal a Dragon card from your hand or choose a Dragon you control.
Dragon's Fire deals 3 damage to target creature or planeswalker. If you revealed a Dragon card or chose a Dragon as you cast this spell, Dragon's Fire deals damage equal to the power of that card or creature instead.

Skithiryx, the Blight Dragon

Flying
Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
{B}: Skithiryx, the Blight Dragon gains haste until end of turn.
{B}{B}: Regenerate Skithiryx.

Arcane Signet

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

Shivan Dragon

Flying (This creature can't be blocked except by creatures with flying or reach.)
{R}: Shivan Dragon gets +1/+0 until end of turn.

Izzet Signet

Drakuseth, Maw of Flames

Flying
Whenever Drakuseth, Maw of Flames attacks, it deals 4 damage to any target and 3 damage to each of up to two other targets.

There and Back Again

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Up to one target creature can't block for as long as you control There and Back Again. The Ring tempts you.
II — Search your library for a Mountain card, put it onto the battlefield, then shuffle.
III — Create Smaug, a legendary 6/6 red Dragon creature token with flying, haste, and "When this creature dies, create fourteen Treasure tokens."

Polluted Delta

{T}, Pay 1 life, Sacrifice Polluted Delta: Search your library for an Island or Swamp card, put it onto the battlefield, then shuffle.

Dragon Tempest

Whenever a creature you control with flying enters, it gains haste until end of turn.
Whenever a Dragon you control enters, it deals X damage to any target, where X is the number of Dragons you control.

Dimir Signet

Xander's Lounge

({T}: Add {U}, {B}, or {R}.)
Xander's Lounge enters tapped.
Cycling {3} ({3}, Discard this card: Draw a card.)

card advantage

Herald's Horn

As Herald's Horn enters, choose a creature type.
Creature spells you cast of the chosen type cost {1} less to cast.
At the beginning of your upkeep, look at the top card of your library. If it's a creature card of the chosen type, you may reveal it and put it into your hand.

Defiant Thundermaw

Flying, trample
Whenever a Dragon you control attacks, it deals 2 damage to any target.

Invasion of Tarkir

(As a Siege enters, choose an opponent to protect it. You and others can attack it. When it's defeated, exile it, then cast it transformed.)
When Invasion of Tarkir enters, reveal any number of Dragon cards from your hand. When you do, Invasion of Tarkir deals X plus 2 damage to any other target, where X is the number of cards revealed this way. (X can be 0.)

Invasion of Tarkir // Defiant Thundermaw

Steam Vents

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

Goro-Goro and Satoru

Whenever one or more creatures you control that entered this turn deal combat damage to a player, create a 5/5 red Dragon Spirit creature token with flying.
{1}{R}: Creatures you control gain haste until end of turn.

Dragon's Hoard

Whenever a Dragon you control enters, put a gold counter on Dragon's Hoard.
{T}, Remove a gold counter from Dragon's Hoard: Draw a card.
{T}: Add one mana of any color.

Brainstealer Dragon

Flying
At the beginning of your end step, exile the top card of each opponent's library. You may play those cards for as long as they remain exiled. If you cast a spell this way, you may spend mana as though it were mana of any color to cast it.
Whenever a nonland permanent an opponent owns enters the battlefield under your control, they lose life equal to its mana value.

Blood Crypt

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

Dragonspeaker Shaman

Dragon spells you cast cost {2} less to cast.

Rakdos Signet

Rivaz of the Claw

Menace
{T}: Add two mana in any combination of colors. Spend this mana only to cast Dragon creature spells.
Once during each of your turns, you may cast a Dragon creature spell from your graveyard.
Whenever you cast a Dragon creature spell from your graveyard, it gains "When this creature dies, exile it."

Scalding Tarn

{T}, Pay 1 life, Sacrifice Scalding Tarn: Search your library for an Island or Mountain card, put it onto the battlefield, then shuffle.

Seething Landscape

{T}: Add {C}.
{T}, Sacrifice Seething Landscape: Search your library for a basic Island, Swamp, or Mountain card, put it onto the battlefield tapped, then shuffle.
Cycling {U}{B}{R} ({U}{B}{R}, Discard this card: Draw a card.)