I'm just double checking myself on a potential ring magic implement set up.

A magic ring that allowed additional target (+1D), range (+1D), and empowered (+2D) would be able to apply this to any spell that met those statistics. So Attack could benefit from range and empowered but not additional target, Barrier would benefit from all three, Curse could benefit from ranged, but not additional target because that is +2D for Curse, and not empowered because there is no empowered option for Curse and so on.

All Attacks are at +2 but all checks are upgraded once.

As far as crafting a ring goes, the only thing I've been able to find on crafting is from Realms of Terrinoth and it seems a ring would be a Daunting check to craft to me (but could benefit from the effects on Table 2-16 if rolled well). I'm considering upgrading that once in the same way the user will have to upgrade their difficulties after its created.

Does that sound about right?

There are a couple of different ways that you could rule when the ring allows its reductions, but what you have said here is how I and all of my players interpret it. It might be reasonable to allow a Curse spell to add the Additional Target Effect for +1 Difficulty instead of +2 as if it were partially covered by the ring, but this is admittedly not supported well by the wording of the implements, just figured that I'd mention it as an option.

As far as the crafting check goes, there are also a couple choices. If I understand you correctly (I apologize if I do not), you seem to be treating the creation of the Magic Ring as a mundane item, which works perfectly well as the simple option, but I would treat it as a Magic Item and use the rules in the GM Guidance: Crafting Magic Items sidebar on pg. 112 of Realms of Terrinoth. So a character would need to first either craft or purchase a mundane ring with the Superior Item Quality (although, going off of the magic items described in that book, the normal benefit of Superior is probably lost when the item becomes magical) and perform a second crafting check with an appropriate magical skill instead of Mechanics to enchant the ring with a difficulty between Hard and Formidable (Daunting sounds right to me for a Magic Ring and, as you suggest, falls in line with the rarity of that item anyway). This way, you can handle the magical side of the creation as its own step, difficult in its own right. The problem with this second method is determining the price and rarity of a mundane ring, because I am not aware if those exist in the rules, but you could always base it off of D&D or something.

It is sensible to upgrade the difficulty of the crafting check to represent the qualities of the ring, but I would only do it if I went with the mundane crafting option, unless I spent a GM Story Point to do so.

Also, just as a suggestion, don't forget to consider the Implement Materials section on pg. 99 of ROT while the character is gathering components if some extra oomf is desired (Willow is a favorite).

Thanks for the thoughtful reply Pratutagus! I'm not to worried about rarity and cost because this is a one off event with very specific circumstances in the game I'm running (there's already a ring made of a unique material that is ready to be enchanted). I've been debating whether it should be an Arcana or a Mechanics check, but I sort of feel like crafting should remain the domain of Mechanics even with magical items. This won't matter for my specific scenario, but what I might do is say that in order to craft a ring you must use Mechanics, but have Arcana of an equivalent skill level available (either yourself or by an Arcana using partner). Such that a craftsmen with skill 4 in Mechanics but only 3 in Arcana treats it as the lower of the two skills, but if they had 3 in Mechanics and 4 in Arcana they'd just use straight Mechanics.