after harrying a column of mercenaries and Night Runner elves escorting Tyr's (secret) levy payment of a thousand slaves to the Dragon's Altar near Altaruk (see skill challenge here:
community.wizards.com/go/thread/view/758... 

, my players found themselves trying to rescue slaves (by rope, and by picking the iron lock on the gate to the altar) as the Dragon appeared to claim his due.
Of course, they ran like hell as he landed and began to drain the slaves of their life-force. As the necrotic drain expanded, I ran a little not-quite-combat, not-quite-a-skill-challenge encounter that I thought I would share here.
The basic idea was that the Dragon's necrotic drain did a healing surge worth of damage each round to characters within range. That means the PCs had 4-5 rounds to escape the range before dying, PLUS any healing abilities or tricks they had (quaffing a potion as they ran, using a healing power on themselves or others, using an action point to get a free move, etc.), MINUS some obstacles that came up on the way. To run it well, I had to try to gauge a "safe distance" that would be close enough to be reachable without getting a TPK, but far enough that it would be a bit stressful.
I estimated that they could generally move 16 squares per round (6 move + run action, double move). The elf and thr-kreen could go a bit faster; the seeker got an extra square from his minor-action shift. Most of them had their action points (so I judged another 8 squares or so) and they were generally fully healed, but short on surges due to a handful of encounters leading up to this. I settled on 300 feet (60 squares) as a safe distance before they could leap into a cave that the Altar Skulker slave tribe had described as safe from the defiling (this also let me leave the Dragon's necrotic feeding range undefined; it was "more than 60 squares"). In the moments leading up to the beginning of the encounter, some of the actions they took led me to modify each character's starting distance by 1 or 2 in either direction (or none). For example, the seeker wanted to try to give one last climbing slave another second to reach the top, so he started at 60 squares away; the mul warden had bolted the instant the Dragon's shadow fell on them, so I let him start at 50 squares from safety.
Each round as they ran, I merely tracked how many squares away from safety they were, writing it with a wet-erase marker on the battlemat next to their figure (but if you had a 60-square battlemat you could actually move them, I guess!). At the end of each round they suffered a surge worth of necrotic damage. Each round after the first, an obstacle arose:
- 2nd round: the characters hit a patch of 4 squares of difficult terrain. They can cross it by running (costs 8 movement points instead of 4), jumping over it (Athletics check/ divided by 5, is the number of squares they can leap), teleporting across it, flipping and springing across it (Acrobatics DC17), etc. Our seeker's silt sandals came in very handy here.
- 3rd round: one character (randomly chosen) slides into a crack. He can free himself, but will lose a full round of movement (one move action and one standard action). If another nearby character assists him, they both lose only half a round of movement (one full move action). I ran this very unspecifically; any character could help the trapped character by sacrificing an action, regardless of how technically "close" they were. It was more a moral choice than a tactical one.
Additionally, on one round (I did it on the 3rd, and bumped the "crack" obstacle to the 4th), you could have the Dragon let out a hideous roar; any character not immune to fear automatically loses his entire round of actions. Only do this if they seem to be intelligently making use of their powers and will reach safety without much trouble; it's a nice unexpected setback.
It went well, and was suitably dramatic (some of them had 1 or 2 hp left when they collapsed into the cave). If a PC falls below 0hp, you could allow his rescue if you choose or allow him to die; if he survives, he can gain a "Scar of the Dragon's Altar" or similar boon power.