More tutorials: http://iwannacommunity.com/forum/index.php?topic=2610.0
I encourage you to open Gamemaker and follow along! You can also feel free to make your own tweaks and additional content to the boss. Here are the assets: https://www.dropbox.com/s/yq9ls0gmdcw8ru5/boss%20tutorial%20graphics%201.zip?dl=0

I made slower progress on the boss than I thought I would. I had three phases planned but only got through one, haha. I also got a bit distracted toward the end, should have wrapped it up sooner.
Timestamps:
0:00 Introduction and getting set up
6:50 Planning the phase and getting started
20:07 Basic cycle complete, next up projectiles
27:56 Projectiles done, next up shooting
31:55 Shooting done, next up rock visuals
40:00 Rock visuals half done, next up misc stuff
45:44 More progress on rocks, next up bird facing direction