Staff of Birdcalls

{t}, Roll a d20:
1-13 — Create a 1/1 white Bird token with flying.
14-19 — Create a 2/1 black Vulture token with flying and deathtouch.
20 — Sacrifice Staff of Birdcalls, then create an
X/X green Goose Hydra token with flying and trample, where X is the number of cards in your hand plus the number of creatures you control.