Whoa, a new best dragon! It seems only fitting that it would be a Double Rainbow Dragon (all the way across the sky...). If you are looking to breed on of these awesome creatures and hatch one of those cool new Double Rainbow Dragon eggs, then read on:
Breeding Pair: (Firefly OR Scorch) + (Seaweed OR Swamp)
Breeding Time: 60 hours or 48 hours (with upgrade)
Availability: Unlimited
Type: Rainbow
Price: 3,125 Gems (It's so intense...)
As I alluded to above, the Double Rainbow Dragon clocks in as the new highest earner among the Epic Dragons, and when it is placed in a Large Rainbow habitat with a partner, the resulting 1000 DragonCash/minute rate reclaims the overall top spot for habitat earning rates (reclaiming the throne from the Large Sun/Moon habitats with combinations of Solstice/Solar Eclipse/Lunar Eclipse/Blue Moon which topped out at 916 DragonCash/minute). So you can sell all of those Large Sun/Moon habitats you just finished making and start building Large Rainbow habitats :).
"Double Rainbow Dragon? I don't even have a single Rainbow!" you say. Not to worry, WOTS has a complete Epics Breeding Guide.
Looking for the full list of limited dragons available right now? Check it out here.