You’re up against a boss fight Nathalia, and not just any boss fight, it’s not even the last boss, it’s the bonus boss that you can’t even beat after you beat the last boss. Shapes such as those are among the most difficult to model. If you tackle it directly, trying to get the shape to work and edges to flow without a template to follow, it is much harder. So what people usually do is first sketch a draft using booleans or sculpting, something messy topology-wise but that gets all the shapes in that for you to later retopo and have a base to adhere to.
Kent has the perfect course for this, he uses all the techniques necessary. It’s an older course but the knowledge is the same no matter the Blender being used:
https://cgcookie.com/courses/modeling-a-sci-fi-helmet-in-blender
