My group found Talon (+1 longsword) in LMoP. None of them would gain any particular benefit from it. The quibbled a bit about selling it, but ultimately they gave it to Sildar to help him defend the town.

I really liked that they did this, and want to reward them in some way. I had Sildar hint that he'd be on the lookout for anything that could help the party.

I was thinking some sort of warhammer for the dwarf cleric. Obvious choice for a fairly equivalent weapon would be to make it +1, but that's not much fun. The player of said character is a big Thor fan, so I like the idea of something with hints of Mjolnir. But left unchecked, Mjolnir's powers would obviously be way OP. 

How about adding 'once per day you can make a 60' ranged attack and the warhammer will return to you'? Does that sound reasonably balanced? More than once per day? Or maybe it's not limited uses, but there's a skill check to catch it on the return? What other parameters do I have to play with? What can I do to play into her Thor fantasy a little, while keeping it roughly equivalent in benefit to a simple +1 weapon?

Side note: She's also the only player in the party that hasn't yet received something cool, and she never makes the "I should have that" argument (not even for the scroll that the others couldn't read and didn't even think to have her look at). Bonus - if the rest of the party keeps sucking all the good stuff to themselves, I can unlock more 'Mjolnir' powers in the future.

I don't see how having a hammer that can be thrown and have it return would be that game breaking in the hands of a cleric. I think I'd do that and then also give it the ability to grant flight for a number of rounds once per day. 

It'd be cool if later you could have a power open up on it that the flight becomes an attack, so basically you can end the flight early by striking a single target and have it do double weapon damage to the target if you hit. 

You could also open up once long rest spells like Gust or Call Lightning much further down the line. 

EDIT:

The Dwarven Thrower is a thing. Just nerf it down to a +1 and call it a day. :)

https://www.dndbeyond.com/magic-items/dwarven-thrower

That's a pretty powerful weapon for a group of 1st to 3rd level players, I'd nerf to just doing the returning function and +1.

I really do like the idea of the hammer opening up powers as the cleric gains levels (becomes more worthy) that way you can always add what ever you want to it and it makes sense :).

First have Sildar either tell the party he heard rumors about blahblah or requests aid with blahblah linked to one of the encounters in the adventure. That way the warhammer isn't exactly a gimme and will feel earned. Be sure to give it a cool name.

You can start with a warhammer engraved with Dwarven runes for strength or power or light. When holding the weapon the user can make the runes glow, shedding bright light in a 30 foot radius, and dim light for another 30 feet. In combat, you can call upon your diety and the hammer shines like silver - all attacks are made as if the weapon were silvered.

At lvl 4-ish attacks can cause an additional 1d6 radiant damage or the hammer flares causing the target to make a save or become blinded until the end of your next turn.

At lvl 8-ish the light from the hammer is Sunlight and your healing spells can affect one additional person.

The Dwarven Thrower, nerfed to +1, seems ideal, and it's perfect that it will only attune to a dwarf. And I can still reserve the right to add abilities to it later on if I decide it's needed. I'll just that in my back pocket for when she's too quiet to push for the good loot, and I think she deserves more than she gets.

I know the normal rules would require an hour of concentration to reveal the Thrower's power, and an hour to attune. But I'm all about the theatrics, show not tell. I'd like it to have a more cinematic reveal, to both her and the rest of the party. I'm thinking the examination and attunement just reveals it as a hammer+1, but "you sense there may be more to this weapon". Then during the next high-stakes combat "you feel a tingle in your arm, and it almost feels as if the hammer is tugging away from you. Instinctively, you know the hammer wants to be thrown." Dwarf (hopefully) throws it, whacks bad guy, hammer whips unexpectedly back into hand, group cheers, player feels badass, etc... I believe my table would get a big kick out of it.

Thoughts? Cool, or railroady?

Well, my daughter (who is the dwarven cleric in question) had a terrible day at school and came home quite upset.

l accelerated plans somewhat and she got the Thrower tonight. I introduced the abilities precisely as described above, and it got precisely the reaction predicted. There was screaming, there was high fiving, she felt like a total badass and the first place her mind went was "Thor's hammer!", just as intended. It was exactly what she needed to cheer her up in the moment.

So thank you all for the part you played in making a 13 year old's night. 

Always warms my heart to hear how gaming has a positive impact on people's lives. You are the real hero here, recognizing her bad day and using this as the vehicle to pump up her spirits. Good job mate.

Congrats!!! Sounds like you figured it out in a fantastic way.  You can disregard the rest of my post or use it at another time if you like.  

Here's a custom made magic weapon I made for a cleric in one of my campaigns.  It gets more powerful as you add different stages to it.  I had it so that every couple of levels they'd find the next piece.

https://www.dndbeyond.com/magic-items/1065308-marthammor-duins-thunderstick

Awesome! (And yeah, the extra damage on the Thrower is pretty stout for low levels, but adding a bit when you throw encourages "cool", and the super-bonus vs. giants probably won't come up much until you get to higher levels anyway.)

I love the idea of the warhammer gaining more powers! What about, say, a 20ft flight speed? The hammer could carry you.

Quote from DougLanglois >>

Well, my daughter (who is the dwarven cleric in question) had a terrible day at school and came home quite upset.

l accelerated plans somewhat and she got the Thrower tonight. I introduced the abilities precisely as described above, and it got precisely the reaction predicted. There was screaming, there was high fiving, she felt like a total badass and the first place her mind went was "Thor's hammer!", just as intended. It was exactly what she needed to cheer her up in the moment.

So thank you all for the part you played in making a 13 year old's night. 

And that, my fellow gamers, is what D&D is all about.