So, for normal conflicts... the attacker chooses the form of the attack and rolls the appropriate dice.
The defender must defend with basically the same setup if they want to be able to inflict Harm with their own successes.
Alternately, they can substitute a different stat, but then any successes can only be applied as bonus dice for the next round. If the chosen stat isn't really appropriate, they'll only get +1d6 per success instead of +2d6 (is +2d6 a good idea? Needs playtesting).
An interesting option is a "sudden twist" where you narrate some factor that lets you get a reroll... such as finding a discarded weapon, sudden intervention by an unexpected ally, divine intervention, throwing sand in your foe's eyes, etc. You can only declare one twist per session and ideally it should be different from any twists declared by other players already that session. A twist renders that contest moot and immediately allows you to start a new one the same round.
If you beat someone by 2+ successes, you can decide to inflict a semi-permanent hindrance instead, such as disarming them, wounding their leg, etc. This penalizes their rolls by 1/2 as many levels as you beat them by, but the effect lasts an indefinite length of time. Disarming might be cheaper because it's easy to undo.
An optional rule, perhaps... you can take a Doom rating. Up to 3d6. For free.
This is when you define your character's Doom (eg- eaten by a cat). When threatened with a different death, you get to add the Doom rating (up to 3d6) to your rolls to avoid it. When threatened with that death, well... you subtract it.
Yeah, it's kind of hokey, but it does kind of fit the grim & gritty part of the setting.
You might be able to get one with a powerful divination... they "look up" how you die and you get an appropriate-strength Doom rating when they tell you.
I liked the suggestion that Mongoose made on RPG.net for a different game...
Use a weapon and shield for a bonus to defense.
Use a two-handed weapon to inflict extra damage.
Use two weapons for a bonus to attack.
So... a shield could easily just be +1d6 to defense rolls (or, if you lose a contest, roll 1d6 to try and subtract a success from theirs). An extra weapon is +1d6 to attack vs foes with a single weapon and no shield. A two-handed weapon is +1d6 vs big foes like most predators... or perhaps an extra success if you win a fight... but that's probably overpowered.
Creating a basic Familiar is a Minor Enchantment of Calling. It's just a well-trained pet for the most part. You can sense its location and whether or not it's in distress, but that's about it.
A full Familiar is a Major Enchantment. It has the additional property that you lose a d6 of Magic, investing it instead in your Familiar. So long as it's nearby, you can include that Magic die in your trait, but when it's away, you can't. On the upside, the Familiar is now basically another character and you can swap between it and your "real" character at will... if the mage concentrates, they can even see through its senses and control its actions in detail. Full Familiars tend to be spooky and very quiet, since they share part of the mage's soul.
Okay, what's the plan to finish off and release Hyperborean Mice?
1. Rule of 7... stick with 7 of each major element. Don't bother developing more unless you've already got it ready. 7 world regions, 7 major kingdoms, 7 races, 7 magical arts, etc. If you can't come up with 7 of something, it's probably not worth being its own category.
7 deities: Lucielle, Lumierre, Duvain, Canduss, Zakarvus, Magellian and Jandara. Plus Quickpaw, of course, but he's more of a folk hero.
7 major areas: The Fallows, Fashor, Rookswood, Greatwater, The Forbidden Lands, The Wildlands and... the Coast? The Underworld? The Swamp? Maybe go with the legendary underworld.
7 dark gods: Hoorooru, Skzentic, Sssaa, Withertail, Sethias the Black, the Ka'ats and I need one more. Perhaps Hellmouth?
7 magical arts: Shaping (includes Healing), Telekinesis, Spark, Scrying, Mesmerism, Illusions and Calling (summoning/telepathy).
2. Don't sweat new art. Finish the writing, then see if you get inspired with examples of additional art that you need. Assume all-text at first.
3. Basic formatting from the very beginning, but that's just assigning categories to stuff. Header 1, etc.
4. Aim for 50 pages. If I blow through that, expand to 100.
5. Use the minimalist system I've thrown together and don't sweat the details. You can always tweak the rules later. Hopefully actually finishing the rules will get me sufficient feedback/urge to playtest to finish the rest off.
So, the outline....
Enchanted items can be very nice, but spells don't stay good forever. Eventually, inevitably, they start to go wrong. This process is commonly known as Going Sour.
Stage 1 (Twisted): the spell now does something slightly different than the original intention. It may not work in all circumstances (for example, an enchanted blade that now gives no bonuses to cut undead flesh) or it may do something related but different (an enchanted blade that now glows, rather than doing extra damage).
Stage 2 (Torn): the spell is now broken in a major fashion, which causes it to sometimes perform the opposite of its original task, usually right after you start depending on it to work. When it does backfire, it often acts twice as powerfully as normal, then ceases to work entirely for days or weeks. For example, an enchanted sword might suddenly burn the user's paw in the middle of a fight or fling itself away from you when you attempt to strike a foe with it. Weapons often become very difficult to put down, applying their magical power towards forcing the user to continuing to hold them.
Stage 3 (Tormented): the spell is now largely independent and malign. The item may go back to performing its original function in a weakened fashion, but most of its power acts as a kind of curse, causing random mayhem and dismay in its vicinity. For example, an enchanted sword might randomly cause its wielder to strike at a friend or even cause stab wounds to suddenly appear in the flesh of a nearby person at random intervals. Tormented items often end up summoning (or perhaps even becoming) demonic entities.