(OOC: I can see why you thought this was tricky :\ The following SBLOCK is more an indication of my ability to understand the scene melting down than anything else--please take it as my failure, not anything wrong with your work here.)
[SBLOCK=OOC]Hmmm.........this one is super-hard for me because I can't build a reasonable in-game explanation for events for Alys to believe. This enemy warlock girl got from the floor to the ceiling just like that without being seen and shot all at once? I'm going to give Alys a Knowledge: Arcana check to decide whether she wants to surrender. Since you listed the Eldritch Blast, I know from metagame that this is a Warlock level 3 or 4, but it's unfair to use that information, and Alys couldn't know of any ways to get to the ceiling like that so quickly without being seen except a suped up Dimension Door/Slide (or weird encounter writing by this adventure's GM, but Alys doesn't know about that possibility), and anyone with a Dimension Door could kill the whole group in one hit with an Area spell for 7d6.
I will set an arbitrary DC of 20 for Sin to be (incorrectly) confident that this teleportation to the roof is a display of unbeatable power. Lower and she isn't sure enough so won't surrender.
Alright, I rolled a
16. This is too low to be confident. She's still pretty shaken up by this, though!
Okay, next questions--How high is the ceiling? Enemy girl is shooting at us, presumably immediately hiding again. Doesn't Alys get a Spot check at +20 to spot her (or at least pinpoint the origin square)? If the answer to all of this is just 'The old GM said that the girl was made invisible by the illusion even though the PCs can see each other and the girl can see them, and the GM didn't explain / used fiat that the girl suddenly appeared on the ceiling', I'm cool with that and I'll stop asking, but could you tell me so I can stop hurting my head trying to think of a normal explanation in character as Alys?
Let me know if Alys sees the girl--if so, she can try to direct the other PCs. If, as I fear, it's the 'plot device illusion makes her invisible' thing and disbelieving the illusion doesn't help, I don't know if anyone in the party has anything better to do than shoot crossbow bolts into random squares (though maybe the others do).[/SBLOCK]