Centipedes crawl out through the new black breach in the veined stone.
The cleric with the 16 Int backs around the corner.
Oh, who knew? The ArchLich has been released. If only someone had been able to read ancient Omnithroxian.
No matter what you, as GM, decide at this point it will smack of GM fiat. You are either nice or cruel. The Archlich can toast them, there's pretty much no doubt.
What's up to you is whether it cares. Does it TPk them all or just howl shrilly, unfurl its gothic wings and find an innocent village or ancient foe to unleash itself on?
There's a fly in the room I'm typing this in right now, but I can't be fucked. Even less so after I just woke up.
|Shire? Baggins? No? I'll just be moving along then...|
So rather than just deciding and being a big softie or a cruel hardass, give the situation some tension using the Indifference Number.
It works like this:
Assuming no specific reason to kill a lesser being or keep it alive, subtract the lesser being's level or HD from the Fearful Entity's level or HD. (Or, if the lesser being is being somehow clever, the lesser being's apparent level or HD.)
The resulting number is the Indifference Number--representing the chance that the powerful being sees the lesser as not worth the effort--then roll d20.
Or, hell, have the player roll d20.
Rolling under the indifference number means the greater being can't be fucked to deal with you, and goes about its wicked business.
The GM should only invoke the Indifference Number when it makes sense and will be interesting. The player cannot reliably evoke the indifference number to save his or her ass.
Modifiers should be made in the case of PCs making a pest of themselves, wearing the panoply of antithetical gods, kneeling politely, or whatever.