Okay. I can answer questions.

How did you acquire this? What are its limitations? How carefully do wishes need to be phrased?

Traded for it from some evil aliens from my world who were using it as an energy generation hack by giving them a better energy generation hack. There's two limits - bandwidth and generation - generation matters less with my hack in the mix and the limit on wishes is bandwidth. Phrasing matters almost exclusively as an expression of intent and the system has some do-what-I-mean baked in but exactly how it does what you mean can vary.

But 'I want the Enemy destroyed' doesn't take half the continent with him, or anything like that?

Shouldn't. It doesn't usually have to go through things to get results, like that.

And if the Enemy has some sort of magic set to trigger when he dies?

Then we go back in time and try again.

...I didn't realize that was an option. That's useful. Is this the first time we've interacted?

Yeah. If it's looking like it'll require a lot of fine-tuning I will want you to write yourself a letter or something.

Alright. 

And someone steps out of the fortress. He is badly scarred, and the look in his eyes is frankly frightening, until it settles on Fingon and softens to something like distant torment. 

Also incidentally I can with regular non-wish magic do healing.

Killing the Enemy will be healing. But you can raise it with him once we've done that.

Hello. My crown prince Fingon explained this. I very much desire the Enemy dead.

Bella checks him and - Yes, yes you do. Do you have a wording you like, what is it? Do you want to make a case for having persistent magical powers post-wish?

Without damage to the rest of Beleriand I want the Enemy and those Maiar that serve him to stop existing irrevocably and forever. Can other people wish me magical powers later, or would I have to include those now?

You could get some fairly specific powers via other people wishing them for you but the whole freeform package me and Lúthien have is with your wish or never. Maybe go with a 'from this day forward' wording in case 'irrevocably and forever' interacts badly with my time travel, there might be fallout I want to retry to avert.

Is the wish less likely to go through if I wish for 'the powers to kill the Enemy' or something that grants a freeform package?

The magic powers have a capacity-per-time limit and I wouldn't want to bet on them to kill an evil god even though I can cheat at per-time, or I'd just go do that. The freeform package can come with any wish at all, but it'll be themed around what you wish in terms of what you can do most efficiently.

Do I need to alter the phrasing of the wish or just have a desired set of capabilities in mind?

Bella, she says anxiously, keep in mind that everything I've heard about him is pretty bad.

I know, I asked if he wanted to make a case and he hasn't actually made it yet, these are all technical questions.

The wish phrasing can and should be chosen independently of whether you anticipate persistent magical powers.

Themed around the wish? So I can't wish him dead and then get a powerset helpful for postwar reconstruction? Has someone already wished mortality gone?

Without damage to the rest of Arda I want the Enemy and every Maia that serves him irrevocably dead from this day forward?

Themed around the wish loosely, but you will probably get something destructive as your particularly efficient power. Everybody gets telekinesis and healing and conjuring some usually-wish-unrelated-but-separately-themed objects and some transmutation and other smallish freeform local effects though. Mortality being gone is not yet addressed but wishes can do resurrections. And that wish phrasing sounds fine to me.

And if the results are unsatisfactory you can reset time and try again?

Yes but I have reservations about it and will probably reserve it for really unsatisfactory results and not 'you don't like your magical girl powers'. - The magical powers thing was exclusively teenage girls on my world. And you still haven't made a case for having them.