Creating NPCs with class levels in D&D 4E

NPCs with class levels and powers are not common in D&D 4E.
I like NPCs in an adventure that are similar to PCs, and I have a way to create them easily.

Zelenna, Night Hag

Zelenna is a Night Hag that grants people their desires but twists them.
She likes to toy with people and eventually wants to create a coven of hags.

Harvesting Monster Parts

Killed Monsters can be harvested for useful parts.
This turns those monsters into rewards for the PCs.

Steal Cockatrice Food quest

Someone keeps cockatrices in her apartment and has everlasting provisions to feed them. Can the PCs steal the everlasting provisions for the starving people in the city?

Vampire in Wine Cellar Quest

The PCs face a vampire who mixes his blood into wine to weaken his prey.
Can they stop him and his thralls?