The Festive Collection

There are five dragons in the Festive Collection:

Paradise Dragon    
Carnival Dragon
Tiny Dragon
Steampunk Dragon
Viking Dragon

Carnival Dragon is a Generation EX-II-b Exclusive Metal and Flame hybrid.
It's not breedable at the moment.
Hatching takes 20 hours.

Steampunk Dragon being a Generation II hybrid is the easiest of these to breed. It's pretty straight forward, flame and metal hybrid. Breeding and hatching take 16 hours.

It is easier to get the EX-II dragons by using hybrids as parents.

Paradise Dragon is a Generation EX-II Nature and Flame hybrid.
Breeding and hatching time are 20 hours.
Both parents need to be at level 10 or higher.

Tiny Dragon is a Generation EX-II-b Nature and Light hybrid.
Breeding takes 12 hours and hatching 16.
Both parents need to be at level 15 or higher.

Viking Dragonis a Generation EX-II-b Ice and Sea dragon.
The breeding and hatching both take 20 hours.
Both parents need to be at level 19 or higher.

The Gaia Collection

There are five dragons in this collection:
Seahorse Dragon    
Plankton Dragon
Aurora Dragon
Deep Forest Dragon
Hammer Dragon

Seahorse dragon
sea + nature
EX-II
Breeding takes 16 hours
hatching takes 20h

Plankton Dragon
Sea + Terra
EX-II
Breeding and hatching both take 20h

You need to have high level dragons to get EX-II-b dragons, preferably on level 20 or higher.There are reported instances when the parents have been on a lower level (like 19...)

Aurora Dragon
Electric + Flame
EX-II-b
Breeding and hatching both take 20 hours

Deep Forest Dragon
Nature + Terra
EX-II-b
Breeding and hatching both take 20 hours

Hammer Dragon
Sea + Metal
EX-II-b
Breeding takes 12 hours, hatching 16

The Legendary Collection

Legendary Dragon    
Wind Dragon
Mirror Dragon
Crystal Dragon

These are all legend dragons, which means they are Generation IV.

They are all breedable, the breeding and hatching takes 30 hours (2 days and 6 hours)

You need to have two pure/pure hybrids to get a legend dragon. It doesn't matter which other elements the parents have, they just need the pure element. I got my Wind with two Basilisks.