Plague based feat for a paladin

[richardbob123]

I'm making feat for a plague based melee paladin and wanted people option on what i came up with so far and how i can improve it

Plague sculptor:

Your mastery of disease and plague, has given it solid form and even deadly potency.

As an action on your turn, you must expend any amount of hit dice, and take half the amount rolled in necrotic damage. When you do this you summon a weapon made of solidified disease, that deals 1d8 necrotic damage per 2 hit dice spent. Necrotic damage dealt by this weapon bypasses resistance

[oogaboogagoblin]

how long does this last? id have it be 10 mins at most because this is a really strong ability if you're willing to waste hit dice.

[Brawnspear]

This feels like it could be based around a dm requested (or approved if you're the DM) change to the Shadow-touched feat from Tasha's.

That gives you a stat boost, a specific 2nd level spell, and a first level illusion/necro spell.

Change out the specific spell for one based around Shadow Blade but doing necrotic damage instead, trading the advantage in dim light for bypassing necro resistance.

Maybe instead of the 1st level spell from Shadow Touched allow the user to burn hit dice to 2 at a time to summon / boost the spell's effective level by 2. That way the user has 2 options for powering the spell, their spell slots or the more risky version of sapping their own life force to empower their attack.

Possibly allow the stat boost to be to Con to reflect the life-force nature of the spell.

So you're left with a feat that

Gives you +1 to one stat
A free one minute use of Necro-Shadow Blade at its base level
The Necro-Shadow Blade spell always prepared and usable in the traditional way
An additional way of powering Necro-Shadow Blade that can take it above even your highest spell slot at the cost of your life energy.