Severe phenomenon

Hello hello! I hope you enjoy the puzzle. This one is not pretending to be an easy one. Thanks to Brooke Husic and Christopher Adams for test driving this one; both gave excellent feedback, and the puzzle is a little less obnoxious thanks to them — well, and a little more obnoxious — OK, let’s say it’s more obnoxious in good ways, you know? Let’s hope so. Enjoy!