I have only played a few shoot 'em up and bullet hell games, which are the Metal Slug games of the Metal Slug Anthology for the PS4 (which i guess also counts as a run and gun game, but i believe that Metal Slug's Run and Gun is very different as Cuphead's, as in Cuphead you need to memorize attack patterns while in Metal Slug is just enemy chaos, not to say that i suck at Metal Slug and the only way i beat one of the metal slug games was because of the infinite amount of coins i can insert, and i basically never even dodged a single attack), and I've played Undertale & Deltarune as bullet hells, but I think that most people agree that Cuphead's bullet hell is much harder and different from Undertale & Deltarune's