I've made a few different versions of Sognirstane over the years for the UK/EU version of the game.
Eventually I settled on the following:
- 2 attack dice.
- You may throw it, but if you do, you can't use it next turn. After that, it flies back to your hand. (Like Thor's hammer... probably taking the long way around the dungeon.

)
- It makes you immune to ALL spells.
- As with other Quest treasures, no restriction on who can use it.
This way there's no need to keep track of which square it lands on, so no separate counter or anything. You can just turn the card sideways or flip it over once you throw it to remind yourself that you can't use it next turn.
I've changed the spell immunity to 'all spells' because, at the time this quest was written, as far as I know, the only spells in the UK game were the elemental ones. There were no Chaos/Dread spells, no UK Wizards of Morcar spells, or anything like that. Bosses used the elemental spells on the rare occasions they got to use anything at all (such as Balur the Fire Mage having the Fire spells). Therefore the elemental immunity made more sense at the time.
The thing about Sognirstane is that it's fairly easy to get hold of, because Halls of Durrag-Dol isn't very difficult and you can potentially play this quest at any time (since it's not part of an official quest progression). I'm OK with the hammer being a fairly mediocre treasure, like Orc's Bane. Using my version, a two-dice ranged attack you can use every other turn is pretty strong.