More detailed feedback on several tokens.
Ring of the Sacred Circle
Problem Statement
The Ring will boost AC, Saves, and for multiple classes add FOPs, which is additive to the set bonus. This means when added with another Arcanum set item, we're seeing multiple relic items consolidated into a single slot, and are likely pushing the values too high with too small of a slot commitment.
Let's look at Arcanum shirt + Sacred Circle w/ set. We get
+2 melee hit
+2 damage w/ melee and thrown weapons
+2 ranged hit
+5 Ref Save
+5 Fort Save
+5 Will Save
+5 AC
14 HP
+2 FoP
+1 level
In 2 items, we get a level, nearly a legendary cloak, nearly a legendary ring in AC (Rolland's), nearly a legendary ring in ref (Khing's), and the the extra add on in Level, HP, FOP, and hit / damage. These bonuses will be very common going forward and we have to consider the ramifications of giving out lots of Saves, ACs, and FoPs in future runs.
Possible Solution
Cut the CHA bonus from the ring, OR remove the free FoP from the set bonus. That way you still get A FoP, but you don't double up.
Reduce or remove the "bonus" AC and saves from the ring OR reduce or remove the bonus AC and saves from the set.
Possible Power compensation
If the ring loses the bonus AC and Saves, since the rings will be numbered, consider allowing the Ring to get access to Eldrich Sublcasses 1/year. This would be a desirable add to let people who missed the boat on the skull to get access to subclasses.