Great ideas!
Updated with Cleon's skill suggestions and freyar's planar commitment.
For the Spellcraft check, maybe 10+spell level vs. each of the known spells?
Sure! Rather than leaving the ability wide open, should we just list several possible applications, including the "recall agony"-like effect and the "rememorize spell" effect?
Are you suggesting the DM rolls Spellcraft checks against every spell the target knows? If so, I think a caster level check or an X+caster level DC is a much more practical idea!