Feedback: magic weapon ability AND spells

[Fizban]

Between the Demonhunter thread and this I almost thought someone was about to try a Warcraft setting. Which already exitsts btw, but that's not the point.

Right off the bat, DC 25+enhancement bonus is excessive, considering that the base DC of a lv 9 spell is 23.

I won't give a specific idea, but rather a host of possibilities that are all much simpler.

Spells lost:
You could simply burn their highest available slot, it's been done before.
You could burn x dice of spell levels, say 1d4, 1d4+2, and 1d6+2, payed in a combination of spells/slots of the target's choice.

Damage: x or x dice/spell level burned is the easiest and best way to do this. I'd suggest 1d4/level is the most you can do without it just being a death sentence (assuming you burn their highest slot).

Save: well, you may or may not have a save, but there's a few ways to determine it if you do:
Flat DC
DC= 10+ damage (or a fraction thereof) dealt by the hit
DC= 10 (or more)+the amount by which the hit succeded
DC= 10 (or more)+the enhancement bonus of the weapon
DC= 10 (or more)+a relevent ability bonus of the wielder
DC= a combination of the above three

Now, for any of these, I would suggest it only be usable once per round, say requiring a standard action to activate and allowing only one attack. It's a very variable ability, either too weak or an instant kill against any spellcaster, so choose carefully.

Edit: also, for your balance consideration:

Mindcrusher

Any psionic creature struck in combat by a mindcrusher weapon loses a number of power points equal to half the amount of hit point damage the weapon deals (only the base damage of the weapon contributes to the power point loss; additional damage from high Strength or other sources does not cause additional power point loss). A psionic creature that is out of power points (or has none) must succeed on a DC 17 Will save or take 1d2 points of Wisdom damage.
Strong psychometabolism; ML 12th; Craft Psionic Arms and Armor, psychic vampire; Price +2 bonus.

Now, the fact that it specifically drains power points makes it a little harder to adjudicate under magic/psionics transparency, but it drains very few spell levels.
1st level spell=1 point
2nd=3
3rd=5
4th=7
So, you're not likely to drain anything higher than 3rd level for less than a +2 bonus, and that's without extra damage.