I just TPKed the group I DM for with a single NPC yesterday. Not surprisingly, I find myself going over the setup and combat to make sure I didn't give them a no-win scenario.
The party: Human Crusader 6 with Stone Power focused on Devoted Spirit, Human Sorcerer 6 with heavy draconic feat focus and blaster-orientation, Changeling ranged Fighter 2/Ranger 4 with Distracting Attack instead of companion, Kalashtar Kineticist 4/Swordsage 2, Elf Paladin 6 who had yet to call a mount, Rogue 1 /Shaper 4 headed to Ebon Saint. Not present were a Human Bard 6, and a TWF Human Ranger with a wolf.
The NPC: Sun Elf Wizard 7 with Extra Spell, an Item Creation feat (wand went unused), and Improved Init.
The slaughter: The party is on a small island that they know used to be occupied by wizards, long ago, to help the NPCs who are collecting the MacGuffin that grows only there. Passive Spot/Listen checks (I assume an 11 plus their modifiers) vs the NPC let him act unseen. He chugs a Potion of Invisibility. Initiative is rolled; Wizard's initiative order has him go second, but because the Kineticist doesn't see or hear him, he waits and Wizard acts. Wizard casts Solid Fog, aimed to snare the whole party. The party inches away from each other toward the edges of the fog, with the Crusader being closest to the outside. Though they had just come from a fairly large city, none had invested in FoM or similar.
Round 2, Kineticist moves closer to the edge of the fog, and Wizard casts Evard's Black Tentacles into the center of the fog. A random roll in the open for positioning says it snares everyone but the Paladin and Crusader. Failed Escape Artist checks for those in the tentacles, Crusader gets to the edge but not out of the fog, and the Paladin shouts to tell the Kineticist - who has dimension swap - that he's free as the others communicate their plight.
Round 3, successful Concentration check and the Kineticist swaps places with the Paladin, who is better able to soak the grapple damage. Wizard casts Alter Self - Wings. Party takes damage from Tentacles as appropriate. Paladin makes a miraculous Escape Artist check. Crusader steps out of the fog and cannot locate Wizard.
Round 4, Kineticist moves to the edge of the fog. Vortex of Teeth from Wizard hits the whole party, dropping the Sorcerer and Shaper when coupled with Tentacles damage. Paladin moves closer to edge, while the Ranger fails Escape Artist check. Crusader is unable to target Wizard effectively.
Round 5, Kineticist recovers a few HP, then drops from Vortex of Teeth damage, which couples with the Tentacles to take out everyone but the Crusader. Lesser Orb of Frost hits Crusader, and he's down.
The raw numbers didn't make this unwinnable, but did spell selection and circumstance combine for a hopeless scenario? Short of fudging, what are the suggestions of the hive mind?