Two Infernal Mounts Now Have Sources

[Magnakilro]

On MMO-C:

Hellfire Infernal (guessing the red one) is the, at this point, traditional mythic Final boss drop of this tier...dropping from Gul'dan on Mythic. It'll probably be 100% drop until next xpac, where the drop rate will be more typical of a mount.

Felblaze Infernal (guessing he's the more traditional green one) also drops from Gul'dan, but you don't need Mythic for this one.

[Holgarr]

On MMO-C:

Hellfire Infernal (guessing the red one) is the, at this point, traditional mythic Final boss drop of this tier...dropping from Gul'dan on Mythic. It'll probably be 100% drop until next xpac, where the drop rate will be more typical of a mount.

Felblaze Infernal (guessing he's the more traditional green one) also drops from Gul'dan, but you don't need Mythic for this one.

Good. the green looks better.

[Valnaaros]

Such was noted in the mount and pet friend. Still a good find, however