3/4/2024 UPDATE: Minor Tweaks, but the big new thing is a new Throw ability.  Read descriptions below

Please check out Keefr's BG3 Creator's Cauldron mod if you're interested in modding, as I used it to learn how to mod.

First let me say that there are some REALLY good Mjölnir mods out there if this doesn't give you what you're looking for please check those out! I've used them all and they are great!  However, I wanted one to be simpler and feel more accurate to the Norse myths and less to the versions more popular today (not hating, though).  Specifically, I didn't want all the lightning and thunder damage on the ones that exist.  In the mythology there isn't any clear indication that Mjölnir did anything other than hit things really hard.  So, that's what this hammer does.  The Eddas do state that the hammer will come back to him if Thor throws it, so that's in here, too along with a few other boosts that I think are appropriate for this mod.
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Originally, I set out to just create a version that was more in-line with Norse Mythology.  We have two primary sources for Norse Mythology and those are the Poetic Edda and the Prose Edda and I’ve read them millions of times and studied them pretty extensively.  In those, we don’t get a lot of info about Mjolnir, but one of the things I wish I saw less of in pop culture is giving Mjolnir lightning, thunder, and flying powers.  In the Eddas, Mjolnir is described to be unbreakable and won’t fly too far from Thor so as to not be able to return.  I actually love the Marvel version of the character (and appreciate other creative takes on Norse Myths), but again, it’s an interpretation and not what the myths portrayed.  So, there you have it - I wanted a Mjolnir mod that was closer to the myths and not modern portrayals so that's what I did.

This mod has undergone a lot of updates and changes in the past several months as I’m learning to find new things in the files and do more things with mods.  I've also changed how I like to play the game through those months and even had a lot of messages from folks asking for certain things.  As a result of all of that, some of the versions have gotten a little wacky and creatively I just don’t like them anymore.  My hope is that what is now available are the final versions and thus the best versions.

There are three versions that I hope will appeal to all kinds of players.  

1) Balanced Might - Powerful but mostly balanced for any play style or difficulty.  
2) Mythical Might - My original vision for the mod and what I would call the "primary version."  Strikes a balance between role-play casual fun and challenge.  I wouldn't call it balanced.
3) Godly Might - this is the OP version.  No cooldowns on the abilities and invulnerable to everything.  This is cheat mode.

You can find it in the tutorial chest.  I'd recommend downloading the mod that allows you to summon that chest.  I don't know how to put it in vendors, but I'll try my best to do that later.

NOTE: I changed the main attack icon in the game to the icon of "tenacity" because it has a hammer in it.  Sorry, but it's a hammer lovers world and you're just living in it :)

A note on why I chose the abilities I did:

"Absolute Might" - This was chosen as I wanted something that represented the common part in myths where it seems that Thor usually just hits something one time and it is destroyed.  There usually isn't a lot of detail about fights that Thor has in the Eddas, so this one hit kill melee ability is representative of that.  To me, the best story in the Edda that exemplifies this is when Thor gets his hammer back from Thrym and kills everyone in the hall.

"Grand Slam" - This was chosen simply because I wanted to have an AOE type attack in the kit.  Perhaps the best inspiration from the Eddas would be when Thor is tricked by Utgard-Loki and his hammer strikes take out chunks of a mountain.  Exemplifying how Thor's strikes can impact the ground around him when struck.

"Throw" - The unique Throw that you get when equipping this weapon exemplifies one of my favorite stories in the Prose Edda, where Thor challenges Hrungnir to combat after he causes a ruckus in Asgard.  Thor famously throws Mjolnir at the giant, splits the giant's stone (which he threw at Thor) into pieces and then obliterates Hrungnir's head, killing him.  I wanted an ability to exemplify Thor's ability to throw Mjolnir that was a bit unique from the normal throw, so this is what I came up with.  

Balanced Might
This version is intended to be balanced for any playthrough and on any difficulty.  It will be one of the most powerful weapons in the game, but it should be mostly balanced for the game.

Damage: 1d12 (Ignores Bludgeoning Resistance)
Boosts:

• Cannot be disarmed (technically, it is bonded to you, but doesn’t show anywhere in tooltip)
• Returns when thrown (it doesn’t say in the tooltip anywhere, but trust me, it comes back)
• Increase Armor Class by 3 (meant to symbolize the defensive capabilities with wielding an unbreakable hammer that can block any type of attack)
• Grants Advantage on all attack rolls
• Grants “Tenacity”, which deals damage on any miss with a melee attack
• Grants “Heavy Hitter” which applies “Reeling” to enemies on melee hits which reduces their attack rolls
• Grants “Grand Slam” weapon ability which does an AOE and adds an extra 5 Bludgeoning damage to the attack.  Recharges on long rests and doesn’t have a cost to use when it is available.
• Grants “Absolute Power” weapon ability which is a powerful single target attack that adds an extra 25 Force damage to the attack.  It only recharges on Long Rest but it doesn’t have a cost to use when it is available.
• Grants an additional "Throw" ability.  You can see the image of the icon in the screenshot picture, but you can hover over it to see that it is a new Throw.  I don't know how to add the stats to the image in the game, so you just have to make note of how much damage it does.  This Throw doesn't have a cost, has a long rest cooldown, and will do a flat 5000 Force damage to the target as an instant kill - for role-play purposes.
  

Mythical Might
This version is intended to be the main file and my true vision for this mod.  It essentially has two one-hit kill abilities that can be used for role-play reasons and it is boosted well above “Balanced Might,” but it still will not put the game on autopilot.  Recommended for more challenging playthroughs or for folks looking for a mix of role-play fun and challenge.

Damage: 1d12 (Ignores Bludgeoning Resistance)
Boosts:

• Cannot be disarmed (technically, it is bonded to you, but doesn’t show anywhere in tooltip)
• Returns when thrown (it doesn’t say in the tooltip anywhere, but trust me, it comes back)
• Increase Armor Class by 10 (meant to symbolize the defensive capabilities with wielding an unbreakable hammer that can block any type of attack)
• Grants Advantage on all attack rolls
• Grants 100 to your initiative.  Basically, it ensures you always go first in combat
• Grants “Tenacity”, which deals modifier damage on any miss with a melee attack
• Grants “Heavy Hitter” which applies “Reeling” to enemies on melee hits which reduces their attack rolls
• Grants “Grand Slam” weapon ability which does an AOE and adds an extra 5 Bludgeoning damage to the attack.  Recharges on long rests and doesn’t have a cost to use when it is available.
• Grants “Absolute Power” weapon ability which is a powerful single target attack that adds an extra 5000 Force damage to the attack, which essentially makes it a one hit kill on anything in the game.  It only recharges on Long Rest but it doesn’t have a cost to use when it is available.  This is something I like to have for role-play purposes, and you can choose whether you want to use it or not.
• Grants an additional "Throw" ability, which is the ranged one-hit kill ability.  You can see the image of the icon in the screenshot picture, but you can hover over it to see that it is a new Throw.  I don't know how to add the stats to the image in the game, so you just have to make note of how much damage it does.  This Throw doesn't have a cost, has a long rest cooldown, and will do 5000 Force damage to the target - killing anything in the game.  It was designed with role-play in mind, but use it, or don't, how you see fit!
  

Godly Might
This version is the OP one.  Many people message me asking for this type of stuff so here it is.  This will make the game very easy for you but it stays true to the main concept of the mod to be simple and as true to the myths as I can make it without making it silly and giving it all sorts of crazy buffs.  The primary features of this version are that the awesome abilities do not have a cooldown, so they can be spammed and you are invulnerable to everything.  Not balanced AT ALL and designed for people who want to just be overpowered, or who want to be able to play through Honor-Mode without stress and to enjoy a fun ride.

Damage: 1d12 (Ignores Bludgeoning Resistance)
Boosts:

• Cannot be disarmed (technically, it is bonded to you, but doesn’t show anywhere in tooltip)
• Returns when thrown (it doesn’t say in the tooltip anywhere, but trust me, it comes back)
• Invulnerable to all damage
• Grants Advantage on all attack rolls
• Grants 100 to your initiative.  Basically, it ensures you always go first in combat
• Grants “Tenacity”, which deals modifier damage on any miss with a melee attack
• Grants “Heavy Hitter” which applies “Reeling” to enemies on melee hits which reduces their attack rolls
• Grants “Grand Slam” weapon ability which does an AOE and adds an extra 50 Bludgeoning damage to the attack.  No cooldown and doesn’t have a cost to use when it is available.
• Grants “Absolute Power” weapon ability which is a powerful single target attack that adds an extra 5000 Force damage to the attack, which essentially makes it a one hit kill on anything in the game.  No cooldown and it doesn’t have a cost to use when it is available.  This is something I like to have for role-play purposes.  
• Grants an additional "Throw" ability, which is the ranged one-hit kill ability.  You can see the image of the icon in the screenshot picture, but you can hover over it to see that it is a new Throw.  I don't know how to add the stats to the image in the game, so you just have to make note of how much damage it does.  This Throw doesn't have a cost or a cooldown, and will do a flat 5000 Force damage to the target - killing anything in the game.  It was designed with role-play in mind, but use it, or don't, how you see fit!
  

Enjoy!