Stirring Bard

Defender
When this creature enters, you take the initiative.
Mantle of Inspiration — {T}: Target creature gains menace and haste until end of turn.

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.)

Green Dragon

Flying
Poison Breath — When this creature enters, until end of turn, whenever a creature an opponent controls is dealt damage, destroy it.

Draconic Muralists

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

Breath Weapon

Breath Weapon deals 2 damage to each non-Dragon creature.

Tiamat's Fanatics

Haste
Myriad (Whenever this creature attacks, for each opponent other than defending player, you may create a token copy that's tapped and attacking that player or a planeswalker they control. Exile the tokens at end of combat.)

Nimbleclaw Adept

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

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.

Avenging Hunter

Trample
When this creature enters, you take the initiative.

Patron of the Arts

When this creature enters or dies, create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

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.)

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.