Nemdrakes

Nemdrakes would be a new foe in the nether forests. Swooping down on you and spitting fire, it can be a formidable foe. They will land sometimes, but still watch out for their nasty tail attack.

They have a coral-ish crest on their head.

Very rarely, an untameable big one will spawn, proving for much more difficult nether survival.

They can also spawn in soulsand valleys, with different colours.

The small ones can be tamed, but you can't ride them. You need to try and force them to land and trap them with something and try to feed them blaze powder. They can be bred, and they lay eggs. 

If you feed a small tamed nemdrake dragon's breath, it will start producing a purple slime in its mouth which you can collect with a bottle. This slime can be used in potions (Nem drakes change texture in biomes, use the potion to make them stay in a certain texture forever) and more importantly: you can mutate eggs with it. Once glowing blue dots appear on a nemdrake egg, it has a chance of exploding upon hatching but also to hatch a new nemdrake that is big enough to be ridden with a saddle.