Jones Thinderwhip if you’re reading this, turn back now!

So I’m DM’ing Descent into Avernus for some friends and am looking at various ways to tempt them into deals and spice things up. I’m also co-DM’ing and wanting to throw things that aren’t in the book in order to surprise the other DM.

The player is a Melee Tempest Cleric that uses a whip, and is very Indiana Jonesy. But there’s not a whole lot of actual trickery for whips bu the book.

Would it be a decent trade off to get the Battlemaster’s Combay Superiority, BUT every combat you have to roll a DC 15 Wis or Con save or have disadvantage for 1d4 rounds due to horrific visions? Is that a decent trade off? Is disadvantage too much?

To help gauge balance, I’m also tempting another player who’s a fire based gnome blaster with Hellfire. While active it’ll pierce fire immunity and add Con mod to damage...but it also reduced max hp by character level. That can’t be healed or restored, until Hellfire fades. Then your max goes back up, but not healed (like Bloodhunter’s Curse).