Our party has an ally, a - errm - Wizard - called "Ralissi". They picked him up in Tazion, in the pyramid, when they reached a stalemate where neither was inflicting anything significant on the other (fire, fire resistance,...). He had been posing as a Charau-Ka wizard - you may recall him from Racing to Ruin. So they negotiated a truce (he's ... very diplomatic) and eventually agreed to travel together to Saventh-Yi.
He proposed to the (Pathfinder Faction) party that if the combined group could defeat the Rakshasa, he was, prepared... to pose as a (charismatic) Serpentfolk figure, and take up leadership of their faction, pulling them into an alliance with the Pathfinders (!).
He overflew the central island, and also landed and quizzed some of the Degenerate Serpentfolk - he told the PCs about the Rakhshasa, so they could plan ahead and not just march in.
Pre-scouting noted the Zombies, so they made an early foray to deal with them and Ugimmo.
The plan involved making a distraction party: 2 PCs and a bunch of Pathfinders launching an attack of crossbow bolts and illusory Serpentfolk across the bridge to inflame the bad-tempered Charau-Ka, then leg it invisibly to the island and join the others, leaving the incensed Charau-Ka to make a real attack on the central island, and thus draw the Serpentfolk to that side.
The Rakhshasa, would, they hoped, be too busy with his perversions to rush out and deal with trivia unless the Serpentfolk felt the attack was going so badly wrong they would take the punishment of their ruler and admit defeat. (The PCs were confident this would not happen, with the only attack route being across the narrow bridge).
So there he was, lounging around, alone and unaccompanied, when the invisible party sneak in. They break cover by attacking... mostly futilely with his high AC and SR, but the Alchemist was able to lob bombs (touch AC, alchemical fire so no SR). Took a few rounds but basically one-sided... if you can't escape and can't dismiss fire, then Bombs are very dangerous.
Then Ralissi transformed into a Serpentfolk, and went out to the Degenerates and declared that he was now their leader!