Smaug

Spyro

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

Lightning:Thor

Black colored fire: Alduin

If female poison, Medusa

Deathwing

Eragon

Drogon

Paarthurnax

If poison, Durnehviir
If it's red, Odahviing

Toothless

If fire charizard

Ice: Viserion (Spoiler!)

If red or fire: Bloodwing

Inferno

Zapdos

Poison:cyanide

Fire: Ruby
Lightning: Sapphire
Poison: Emerald

Lightning: Chidori