ok so a little bit of background I'm running a tweaked version of call of the netherdeep, I let all of my players pick from a starting magi item, and one of my players decided to take the cursed sword of vengeance because it fit the roleplay for his warlock that thinks he's a paladin that is unknowingly in a pact with the vengeful spirit of his father, and then he really lent into the roleplay for it.

so I've decided that I want  to reward him for that while still leaning into the idea that it is a cursed item by having it grow in power as the campaign progresses essentially like a custom vestige of divergence/arms of the betrayers.

and I just wanted some feed back on the first tier that it will unlock to

https://www.dndbeyond.com/magic-items/5397130-last-embrace-dormant

so what do people think?

Seems fine to me. I guess one of the big unknowns here is the 'indefinite madness' effect, but overall I don't think it's going to break your game or anything.

It does set up kind of a weird situation where he's often making a saving throw that he wants to fail. Certainly an interesting dynamic there.