Yea, there have been a few of these some of which I posted encounters in already so I will try and keep these short...
One
This one is actually from a post of mine on RPGnet...
I had one where the PC's were in a Fort that was sentient and could manipulate various rooms and walls. They went up against a solo construct I made in one particular room. The construct would bend down from time to time (on recharge) and lock his hands into the floor (they would temporarily meld into the floor) and the room would swivel a random direction @ 45 degrees. The players had to make (iirc) an Athletics roll to remain in control (not fall prone), and then a STR check to hold tight - otherwise you would slide in a straight line to the tipped side and take falling damage (and fall prone) at which point the room would correct, and the construct would stand.
I thought it was an interesting way to have the creature roll recharge, and yet the ability represented intervention from the Fort (by tilting the room). The players loved it.
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Two
I want to (and will do) at some point this encounter that I thought of based on a Rush Hour movie (first one I think) - one where, in the Museum, the enemies push over the ancient Chinese vases, etc. In the encounter, like in the movie, the PC's will want these to not be broken of course, but if they do break, they leave difficult terrain in the area.
So mobs push these artifacts (when not attacking them directly) towards the players to hit them (for damage) or away from them to distract them (knowing the PC's will try to save the artifacts). The mobs will have the ability to push an artifact as a recharge power (5,6).
In the case below, the enemy (E) could push the artifact (X) on top of the player (P) or in the square North or South of the player...
0 0 0 0 0
0 P X E 0
0 0 0 0 0
In other words, the opposite square from the enemy or one of the two squares on either side of that (all marked below with a - ) which are also adjacent to the artifact...
0 - 0 P 0
0 - X E 0
0 - 0 0 0
or
0 - - 0 0
0 - X 0 0
0 0 P E 0
or
0 0 E 0 0
0 0 X P 0
0 - - - 0
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Three
I once ran an encounter where an NPC needed to cast this cleansing ritual. He also needed someone to read from a scroll while he did this. This would be an attempt to cleanse this dark orb and seal a portal it was keeping open near it.
But also, he needed people to stand in very specific places (squares) and not leave those squares.
He began and things started to come out of the portal (in this case these crazy Dire Crows I made way back last year before the Monster Builder etc). So, the one reading the scroll had to continue reading, despite being attacked (and had to roll to keep from being interrupted). The others could fight, but again, could not leave their square. Eventually he finished the cleansing and yelled that one person could now move about, but the rest had to stay and the one reading the scroll had to keep reading - at that moment a few demons came out (forgot what I used) so the Fighter (who decided he should be the mobile one) jumped in and tried to keep them off the NPC, etc.
Anyway, that was a fun one as well.
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Four
This is one I am about to run (Brad L and Aaron C skip this)...
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.
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The players are in a pocket dimension that exists "within" a powerful NPC (one they interact with from time to time, though he doesn't help/hinder them really). Within this dimension, he has control over most things, but he is currently very ill and so things are getting a little twisted and they can't get out until they help him.
The players need to travel to a temple (still inside the NPC's dimension) that (for the NPC) represents hope - it's his memory of a temple that once contained a fountain of healing energy. Anyway, on their way there in a carriage, they will be attacked by dark figures riding on the back of what would look like a giraffe. These 'giraffe' creatures however have trunks like an elephant and will, while running along side the cart, be tugging at the wheels trying to make it crash. So there will be those to fend off, plus the cart must be driven (aimed) to avoid obstacles that, if hit, could cause players to fall prone on top of the cart, etc. Stopping will be bad as there will be hordes of things chasing them that can only maintain the same speed as the cart (or less).