I was trying to think of what dragon legendaries could port over into Battlegrounds. These were the ones that stood out to be interesting.
- Emeriss: Certainly a 6 Star Card, Doubling the health and attack of minions in the hand is insanely strong and can certainly snowball fast which is why it should be a final tier option so it can get out of control super fast, obvious risk though is since it buffs cards in hand, they won't be doing much until it enters the battlefield and Emeriss on it's own doesn't do a lot (just a neutral 8/8).
- Zzeraku the Warped: A Token generator on taking damage, which can synergise with Demons certainly. If you have a space spare, get a coin with every trigger of Wrath Weaver. I'd probably make this a 5 star card.
- Brightwing: Get a random legendary, it's stronger than Zerus because you can use it instantly and either get a 3/2 on board or 1 coin on the sell. Make it 4-5 stars. Maybe too strong with Brann though. Might need weaker legendaries in the game to balance it out (or change it's text like they do with Sneeds).
- Chillmaw: A counter to Divine Shield builds which can help against Murlocs. I would make this a 4 star card because it would be too dominant in the early games.
Also here's one Dragon Legendary I
don't want to see in Battlegrounds.
- Onyxia: Basically allows for full rebuilds with 2 higher tier cards if you sell everything just from the 2 Golden Whelps you get. That's maybe a little too much to actually attempt to play around.