Here we have a pool of lava with floating stone islands, walkways and the like. The party shadowdancer appeared at one end to take a look at what was going on, and here is what he saw.
The walkway began to recede as soon as they began. It would sink slowly into the lava, and the only other avenue besides retreat was to cross to an opening at the end of the path. The black tiles were safe while the red and orange tiles on the path did damage and required a reflex save or move at 1/2 speed due to blistering feet. I anticipated the party either running the gauntlet straight along the path or they would deal with the bad guys then airwalk to the exit. They choose the latter, and I had considered more and more critters showing up to attack them to get them to move it along(fiendish manticores aloft and fire salamanders below), but the dragon didn't want to sacrifice any more of her resources to them.
On each of the larger stone islands there was a sorcerer, cleric and a large fighter. Using Enlarge the fighters became huge so they could bull rush or grapple then jump into the lava since they were immune to it. I thought of using the big guys to bull rush the party off of the walkway, but they didn't go for it. The narrow stone bridge allowed the bad guys to walk from one island to the other and also blocked the use of a mount on tile walkway (paladin on warhorse). Fire spells were in abundance, and it was a good thing the party used mass resistance. At first a few of them charged in, but then they started to get beat on a little so they retreated. The baddies used a wall of fire to block them out.
After a quick breather, both the party and the bad guys had buffed themselves up nicely. Then the wall of fire went down, and the baddies launched fireballs up the corridor where the party was hiding. After two rounds of them, the party came out swinging. The bad guy sorcerers used pyrotechnics on the lava to spit up some sparks to blind all but the druid, and he guided his summoned critters to victory.
The fight was 17 rounds long, and by this time the tile bridge had sunk into the lava completely. They used air walk to make it over without getting burned.