[3.5] Invocation. Need Help.

[AustontheGreat1]

Basically it's telekinesis, but it can be attacked and it deals the warlock backlash when it is destroyed.

Please help me make this work.

Dark Grasp
Greater, 7th

The warlock creates a massive hand which is seemingly formed from pure darkness or a swarming mass of insects or bats (Flavor optional.)

This hand can be used to perform any task that could be performed with the Telekinesis spell. This spell creates an actual physical manifestation which can be attacked. The hand has an AC equal to 10 + ½ the warlocks caster level + plus charisma modifier, a number of HP equal to twice the warlock’s level, and DR 10/Magic. If the hand is destroyed, the backlash of dark energies deals the warlock 1d6 damage and the warlock cannot reform another hand until he has taken an 8 hour rest. The utilization of this power requires the use of one of the warlock's arms so the warlock may not perform actions which require fine manipulation or two hands in conjunction with this ability. A warlock may only have one hand manifested at a time, manifesting another hand destroys the previous hand; the hand stays manifested, though not necessarily utilized, for 24 hours or until it is destroyed.

[Waargh!]

Specify what action is need to control the hand. Probably the same as a telekinesis spell? Specify that if you invoke another hand the previous is destroyed. This way the Warlock can "heal" the hand by invoking another one, but not have more than one.
I would change the penalty for being destroyed by making it reusable only after an 8h rest. Having CHA damage is kind of harsh. Having telekinesis all the time is not that powerful. It is more useful outside combat which makes it fine to exist for the Warlock without having a penalty for the hand being destroyed. Being destructible is a good idea, to offer a way for creatures to free something grabbed from the hand.

[AustontheGreat1]

So does it need anything else to work?

[Fizban]

The hand is incredibly fragile and if destroyed you can't use it until tomorrow: I'd never take this. The Crawling Eye/Hand invocations take 1d4 hours, but they're smaller and less direct so you can keep them out of harm's way.

What are you looking for in this invocation? Telekinesis effect, or giant hand effect? If telekinesis, I'd just make it a standard at-will greater invocation, maybe dark if you're really worried. It allows a save or AC to negate depending on how you use it, and lifting things isn't really overpowered.

If giant hand, I'd look at the spell Shadow Hand, which does just what it says. Shadow Hand creates a partially real hand that will give you cover, carry things like a Floating Disk, or grapple, but it's very bad at cover (+4 AC from cover instead of -10 attack penalty like Interposing Hand) and grappling (doesn't have a strength bonus). You could pump up the Shadow Hand or do something like Ice Claw where it has a lower strength but deals cold damage while grappling.

[AustontheGreat1]

Dark Grasp
Greater, 7th

The warlock creates a massive hand which is seemingly formed from pure darkness or a swarming mass of insects or bats (Flavor optional.)

This invocations functions identically to the Telekinesis spell, except that while affecting a target the hand becomes solid and partially real and can be attacked and damaged. The hand has an AC equal to 10 + ½ the warlock's caster level + plus charisma modifier, a number of HP equal to twice the warlock’s level, and DR equal to the warlock's class level which is penetrated by magic. If destroyed, the hand cannot be reformed for 24 hours or until the warlock has taken an 8 hour rest. When the warlock is actively using the hand, it occupies one of his arms so the warlock may not perform actions which require fine manipulation or two hands in conjunction with this ability. The warlock may only have one hand active at a time, reusing of this invocation does not conjure a new hand but it does fully repair any damage done to the hand currently active.

This version seems much more coherent.