2018-10-22, 10:56 AM (ISO 8601)
Re: What to do with random tiny rune cube my player found last night?
Well, you could go with the Infinity Stones idea.
Not the actual Infinity Stones, but more like an Item Set (like they have in Magic Item Compendium). Each one is a specialized Ioun Stone. Each gives a neat little benefit, not listed in the standard Ioun Stone list. They only work if they're unlocked (unlocking mechanism: cast a particular spell onto them; Identify or Legend Lore to figure out what the spell is). Once the spell is cast onto them, they start functioning and flying around the user. If you have several (usually 3 or 5 pieces is the threshold), there are resonance bonuses.