Alavaster, the Flightless

As long as you control 4 or more creatures with flying, Alavaster, the Flightless gains flying and hexproof.
{g}{w}{u}, {t}: Populate. Bird creatures you control
gain indestructible and unblockable until end of
turn.
"If only for a moment... on borrowed wings."
— Alavaster, the Flightless