
ANebulousMistress |

I'd rule the eidolon comes back possessed.
More importantly, though, what sore of damage would this do to the eidolon long term? Can the vilkacis ever be destroyed? Will the eidolon think it's still possessed every time it's summoned?
Will the vilkacis stay in the eidolon's pocket plane (or wherever you have it go) forever? Will the eidolon come to fear returning there because it knows sleep means it's forced to grapple in unending bloody battle with the creature now sharing its nest? If that's the case, what if the eidolon loses that battle? Will the summoner now have the vilkacis as its eidolon? Will the eidolon poke and beg and conspire to keep the summoner awake forever to keep from having to go back there?
This is supposed to be a horror campaign, you've set yourself up for the motherlode of all nightmares. Use it!

Mr. Damage |

I'd rule the eidolon comes back possessed.
More importantly, though, what sore of damage would this do to the eidolon long term? Can the vilkacis ever be destroyed? Will the eidolon think it's still possessed every time it's summoned?
Will the vilkacis stay in the eidolon's pocket plane (or wherever you have it go) forever? Will the eidolon come to fear returning there because it knows sleep means it's forced to grapple in unending bloody battle with the creature now sharing its nest? If that's the case, what if the eidolon loses that battle? Will the summoner now have the vilkacis as its eidolon? Will the eidolon poke and beg and conspire to keep the summoner awake forever to keep from having to go back there?
This is supposed to be a horror campaign, you've set yourself up for the motherlode of all nightmares. Use it!
That's a great point about the horror element!! I wonder if I can corrupt the Eidolon in some fashion so that it takes on certain aspects of the Vilkacis. Maybe the spirits fuse into a sometimes uncontrollable beast. Maybe the summoner loses control, periodically, over the eidolon. Definitely something to think about.