Gameplay Since most of the bosses are fairly stationary, the healing/charging mechanic is interestingly implemented because even if the player could wait until a simpler attack sequence to begin, they will also get locked out of their offensive ability which could potentially encourage them to go for a risky charge, or keep playing it safe and take a longer time whittling down the boss’s health.
I’m not sure if this is the case, but the bullets seem to do flat damage, regardless of where the boss is hit. Since bullets also use up the speed meter to be fired, maybe consider adding small weakspots to reward players for properly aiming their shots.
Misc As for the sound effects, maybe consider adding slight pitch variations to make them sound less repetitive.
Anyway, the gameplay itself is pretty fun and the idea of a mech-y spinning top is great. Congratulations on finishing your entry!