There are 5 size tiers that contain a total of 11 dragons. Listed below are the different dragons along with their abilities.
Tier XS
This dragon gets a 2X multiplier bonus during Fire Rush mode and can partner with 1 pet.
Nibbler
Tier S
These dragons get 3X multiplier bonus during Fire Rush mode and they can partner with up to 2 pets.
Mad Snax
Sparks
Tier M
These dragons get 4X multiplier bonus during Fire Rush mode and they can partner with up to 3 pets.
Don Drago
Jekyll and Fried
Zhe Long
Tier L
These dragons get 5X multiplier bonus during Fire Rush mode and they can partner with up to 4 pets.
Blaze
Dante
Jawfrey
Tier XL
These huge dragons can easily destroy the giant enemies. They are unlocked by unlocking ALL the dragons (XS, S, M, L).
Poseidran
Dranconis
The video below is a montage showcasing each of the dragons.