Damage is the way that most Dragon decks win, so a one-sided damage doubler should be a welcome addition to the archetype
Reaper King is interesting in that, on its surface, it's a Scarecrow lord that grants Scarecrows +1/+1, something we had done many times before
While some longtime Magic players feel that adding characters from intellectual properties outside of Magic: The Gathering detracts from their ability to immerse themself in the game, its hard to argue with results, and The Lord of the Rings: Tales from Middle-earth reigns as Magics bestselling expansion set of all time
Maybe Boros Reanimator with Plargg, Dean of Chaos could use it well since it can get snagged from Plargg's trigger or just throwing it in a Giant deck as a good value creature
Two-Headed Coin The first time you flip one or more coins each turn, those coins come up heads and you win those flips