| To add to the 'playing on player expentancy' comments above, I had a situation with a ritual in my present game.
The PC's were trying to stop a Drider creation ritual. It was a skill challenge during a battle. All the enemies were young Drow children (Reskinned minions). The altar was a fairly elaborate puzzle that prevented the PC's easy access to the top of the altar where they could free the Drow woman who was to be transformed.
Little did the PC's know that the Boss and all the tough hench men had been deliberately distracted and called away by the same mysterious forces who had caused their group's involvement in the first place. The children were actually stopping the ritual until the boss returned. As each child fell beneath their swords the dark cloud swirling above the chained woman became more real and more spiderlike.
Wrongly, they believed time was running out and redoubled their efforts to slay the children in order to stop the ritual. As the last child died they unwittingly unchained the summoning ritual that they had hoped to stop, which they quickly realised as the woman began to scream in excruciating agony.
The puzzle hadn't been completely unravled at that stage and as the woman began to die screaming above them beyond their reach, a very enjoyable and exciting tension was created and it became a real race against the clock despite their victory.
I didn't have any world shattering plot lines hinged on the ritual succeeding and in the end the PC's were able to free the Drow and flee. But them unchaining it could be enough and then the disastrous effects are instantaneous.
I did however give clues to what was going on as they got closer and closer to putting their foot in it. They payed no heed... your PC's might be a bit more switched on than mine (all very new to RPG that seem to blunder into every trap time after time).
Maybe they can't stop the ritual but they can achieve success by taking something from the bad guy that will give tham a distinct advantage in the future or disrupting it in some way, lets say, creating a stitch in time that buys them a few years to foil his plot before the ritual ever takes place.
I guess situations like this are why I prefer to have things lightly sketched out in my head based on the variety of ways that I imagine things might feasibly go. Until I know for sure where things have gone I don't fill things out. That way I haven't invested hours and hours on a story line that never was.
As one of these lightly sketched out options, build in some way the PC's can be successful (without necessarily destroying the villain, and maybe only delaying the inevitable... unless they complete some other heroic adventure in the mean time) into the encounter/story. And I guess, be prepared if the PC's come up with a different way of being successful that you weren't prepared for just in case... the villain can always have an escape route prepared even for the most improbable event of something getting in the way (turning insubstantial or teleporting away to fight another day)...
__________________ 'I am a predator...the predator improves the race...I kill but not out of hate.' Frank Herbert: Emperor God of Dune |