One aspect of Metroidvanias that I feel most people don't talk about is the boss fights. In these types of games, bosses are very techinical in a dodge into attack kind of way. Shantae is an interesting case because some bosses (like the squid barron) follow this rule. You have to learn what they do and counter, however other bosses (like the hypno barron) adopt a far less interesting stand there and hit the attack button while occasionally moving around strategy. Also, I'm 74% certain that they just forgot to put a boss in here. They set up the Ammo Barron for a boss fight the best out of all the barrons and then you just... don't fight him.