Explanation: I had a "big boss" situation with a level 3 party (of 6) that story-wise would work well if they encountered a creature that could petrify. In practice, it worked out great but it was a bit tense. As a backup plan, the local temple had a scroll of Remove Affliction on hand that they were willing to cast at a reduced rate.
I took a level 10 elite medusa and deleveled it to 5 (against a well-balanced party of 6 players), with a very small group of level - 2 minions and level - 1 brutes. I also gave PLENTY of hints that they were about to fight something with stoning power - lots of statues perfectly shaped like people cowering in horror or fighting, etc. In practice, a level + 2 elite -anything- might be a bit much, just because the defenses are high enough that any attack rolls that are less than ~12 miss, and it tends to hit on ~9 vs. AC and ~5 vs. Fort. Give it an at-will stone power and a few low-level minions/brutes to get in the way, and it becomes quite a dangerous situation. But I was ready to fudge some rolls if necessary, and the terrain (cavern with lots of places to hide behind / block line of sight) favored the party.
As it turned out, I fudged nothing. The party was hyper-aware and very focused, and they executed a nice pincer attack on its position (which the rogue scouted) - and in my experience with 4.0 so far, positioning is crucial. They focus-fired on the medusa as soon as they spotted it, mainly using dailies followed by action point-fueled encounters, and they took the thing out in two rounds. (Seriously. They also have two strikers and a defender spec'd for single-target damage.) They pretty much never missed, but that was due to some very good rolls and a warlord that boosted action point attacks. As it was, the medusa got off one gaze that missed one and hit two, and between the cleric's item daily power (+5 to saving against 1 effect) and the heal skill (standard action DC 15 to grant a +2 to an ally's next save), they pretty much knocked it out with decent rolls. The action was intense but everyone seemed to have a good time. (On the other hand, I could easily have seen it swing the other way, especially if the dailies had all missed and the medusa was in a position to gaze several times - and so I was prepared for that as well. This would not have been a TPK regardless.)
Two interesting rules things that came up: from behind the screen, when I deleveled the medusa I decided that its poison attacks - which, according to the rules as I could understand them, wouldn't change - did 5 poison instead of 10 and since I was reducing all damage by 2, I took out the -2 to Fort saves. This never came up (she didn't gaze anyone that had been poisoned) but it seemed more fair. From in front of the screen, I ruled that opening/closing your eyes is a free action that can happen on yours or an ally's turn (if they tell you open them), but I was prepared to ready an action if this turned into an abuse. Or just pummel folks with arrows (and low-level brutes) with combat advantage. If I had to do it again, I think "avoiding looking at her" should probably just give a +2 bonus to her defenses for attacks against her, and a +2 to hit characters with regular attacks and -2 to hit with a gaze; you have to decide on your turn what you're trying to do and it just lasts all turn. Other enemies or ally effects ("if you can see an ally" stuff) are unaffected. This seems like a better balance (and simpler), although it's generally not a good idea against elites or high-level stuff since they already have high defenses and good attacks. But, in the end, it didn't come into play and a good time was had by all.
Thanks for the Dungeon 160 note, even if I didn't see it in time - I'll have to give that a look.