[3.5] Cursed ring of headaches (not the actual effect)

[Dreadgrim]

I devised a cursed ring that gives +1 spell slot of the maximum available level to any divine caster, but forces Concentration checks upen ANY spell being cast. Failure means the caster loses the spell and the action, distracted by the dread voices in his or her mind.

I'm sure this is not balanced, as it's easy to find lots of ways to buff Concentration.

The level 6 Druid in my campaign is wearing it and this almost costed her life.

What do you think would be a decent DC for casting spells with it? Only two rolls she made last time were a 4 and a 5, was going to fail anywyay, I can still fix it or get closer to fixing it.

At the beginning I thought 15 + (2 * Spell level being cast), but it's too low and it doesn't scale well.
Maybe 15 + (3 * Spell level). It gets to a whopping 42 for 9th level spells, but then again a 17th level druid will have +20 ranks, at least +4 CON, and who knows how many other things.

On a side note, I would really appreciate if someone showed me an actual, realistic count about concentration optimization using options and items in the various books, as my knowledge doesn't span them all..

Many thanks.

[LordHenry]

Personally, I would never use such a ring. +1 slot is just way too weak for a chance that my spells fail.
In general, such a mechanic is difficult to implement, but can be very interesting. I'd suggest a fail chance of no higher than 10% (= on a 1 and 2) and quite frankly a more potent effect to make it worthwhile.
Also, maybe find a way so that it does not affect every spell he casts... or sooner or later some spell will fail. And then we are back again to the same old question, why somebody would use such a ring in the first place...

[Dreadgrim]

I wanted it to be negative. It's a cursed item that tries to get you killed. I put the consolation prize of the +1 slot just to tempt the player. I gave them other items that are blatantly negative, this one casts a shadow of doubt. There is already another greedy player wanting to use it if the current owner manages to get rid of it, and the new owner will not even be a proper divine caster, just a Factotum/Chameleon XD

..yes, I am an evil DM.

[LordHenry]

In that case I would go with 15 + (2* spell level).