Post game report:
The party caught one of the servants while he was out shopping - the rogue impersonated him through a hat of disguise and knocked out the other servant, letting the party in.
Predictably, they attacked the armours, alerting the wizard. They send some summons first, which were caught in the tentacles but allowed them to dispel those without harm to themselves.
Then they tried to bypass the stairs by having the druid polymorph into a large bear and serve as a living ramp for the others to climb to the bedroom trap door. This was actually a pretty bad move, as it took the close combat types a whole move to climb up, surrendering the initiative to the fully buffed bard gish upstairs. (they failed to anticipate that danger, despite having learned about his presence by interrogating the servant)
One of the characters died in the ensuing storm of dice, before the bard went down, followed by the wizard, whose spells were all saved against (though the party mage had a close shave with becoming a frog) - an area dispel knocked out the villain's improved invisibility - he promptly crit-failed his will save against a reciprocal gyre and with 8 buff spells still on him, fried in one shot.
