Smaug

Fire: Scorpion
Lightning: Raiden
Poison: Reptile
Ice: Sub-Zero

Spyro

Black colored fire: Alduin

Lightning:Thor

If female poison, Medusa

Deathwing

Eragon

Drogon

Paarthurnax

If poison, Durnehviir
If it's red, Odahviing

Toothless

If fire charizard

If red or fire: Bloodwing

Ice: Viserion (Spoiler!)

Fire: Ruby
Lightning: Sapphire
Poison: Emerald

Inferno

Poison:Adolf Spitler

Zapdos

Lightning: Chidori