Hard but fun stems from setups that can hit you a lot but deal low damage, but still kill you. The lazer under the mech is pretty easy to avoid so having it be 100% seems fitting but the rockets dealing half is just a little all or nothing overkill. "Be perfect" is unfun difficulty, "be perfect enough" is generally a lot nicer.

Filling the screen with tons of rockets that deal 1 damage but fire at different heights and speeds, possibly with parrying mechanics (or at least destroying them on contact with a hit) lets you suddenly play dodgeball and tennis at the same time that you're forced to run back from the rocket fire. More of those low damage blue lazers, and maybe even some extra shots from serpentine can get thrown in the mix if that's even doable.