Spawn of Tiamat:

The creation of demon-dragon hybrids have never been seen before.

Greenspawn Razorfiends:

The party met their first one outside of Drellin's Ferry just before the town was razed to the ground.  The goblin ranger, Wyrmlord Saarvith, was breeding a hatchery full of them in Rhest with the intention of using them in the Red Hand's army, but the party destroyed them all.