Basically, I was reading through my brand new copy of 'Trail of Cthulhu' and realized that there are no spells in Arkham which requires more than one person to cast. While all of them take at least one person (obviously) and you can get Outside help (Lurker) you really can't co-op spells like you really, really should in the Mythos.
Then I reason, there's no spells big enough for that. They all are fairly small and anything you could consider a 'Ritual' is pretty much a Mission or Task. So, I decided to try something new and make a 'Spell' that required the grouping of all Investigators working together. The result is a Scenario--but not quite. And it's not quite a Guardian and not quite an Institute. Therefore, not knowing where to place this, I am putting it here and in my Creations thread. I might try and cook up other 'Ritual' cards and would like to see others do the same, especially folks far more cleverer than I!