I left the ability vague so that people could envision it any way they want really, also it's in true tlopo/potco fashion to have an ability's description be as vague as possible lol
As for it being rank 5, I dont really know exactly why I chose this. Leviathan has rank 5 Leviathan's curse and Soulweaver has rank 4 Watcher's visage, both skills unique to those weapons. -And since I put no thought into what the charge up time, damage output, or additional effect "Devil's Tremor" would have when making it, I decided to just go for it lol
And finally yeah, I agree that wither can be very annoying and unpleasant on the eyes, but seeing as how wither has been buffed on test I really wanted to make a staff with it. The overall staff buff in general prompted me to make a staff concept because the change genuinely made me excited to use and see new staves implemented. I do believe they should have some sort of mini overhaul, but nothing too major.