Hi there,
I use Kroot hounds as Khymerae and the Warmaster Dark Elf Hydra as a Razorwing Flock. The Hydra isn't flying, of course, but I like it because it looks just like a Kroot hound and has exactly five heads (for a 5 A, 5 W model,
GW only gives you 4 birds for each flock base!).