Skree, the Mightiest Birb

Eminence - Creatures with Flying, in all zones, are Birbs in addition to their other types. Birbs have the following keywords depending on the number of Birbs on the battlefield: 2+, Vigilance; 4+, Haste; 8+, First Strike; 16+, Indestructible; 32+, Hexproof.
Flying
Birbs get +X/+X where X is the total number of Birbs on the battlefield.