So ... I'm always a fan of horror, and I think this will play well in helping counter unga-rushes.
Name: Scarecrow / Banshee
Evolves from: T2 Burrower / Hivelord
Uniqueness: Uses a terrifying tele-pathic screech to deafen and stun marines (much like the queen's screech)
Abilities:
Hide/Camo like a lurker can
Screech like a queen but with a lesser effect
Strengths:
Doesn't appear to be incredibly large like other T3's
Is relatively fast compared to ravager, but obviously not as fast as Ancient Runner (420)
Weaknesses:
No armor plate
Does NOT knock-down marines affected by it's screech like the queen