Players getting cocky (4e)

[Vyvyan Basterd]

Now their walking the streets of Calimport with some swagger feeling unstoppable and I think its high time I brought this frame of mind crashing down around them like flaming timbers.

My answer? The Mists of Ravenloft.

*Barely letting them sleep because of constant attacks (from The Twisted Rune so they can't refresh all those daily powers/healing surges is a good start.

*It's bad to have the attention of villains (The Twisted Rune) who would rather just toy with you then kill you outright.

*The <organization inspired by the Vistani>, who are more likely to trick, lie to, or steal from the players, while informing The Twisted Rune about their weaknesses, strengths and actions in Barovia.

That being said, how would you, as a DM, deal with a party that has become overly confident?

You've got some good ideas of how you want to challenge the party. I just don't see why you would want to ruin the pacing of your campaign by shunting it off into a Ravenloft sidetrek. Unless, of course, you haven't mentioned the fact that you used foreshadowing to lead down the path of the Twisted Rune effecting life in the Realms from their home in the Dread domain. You can still use some of the ideas you have regarding Strahd simply by changing the antagonist as I have in the quoted text above. Other changes might require more work to develop the Twisted Rune and the locations they hold sway.

 

[Dannyalcatraz]

Dead Brats often turn campaigns into Outlaw campaigns...at least, short term.

 

[Lord Ipplepop]

I was part of a group a while back that had 4 dm's... the main DM was a Montey Haul kind of chap who made it possible for a 5thy level party to utterly destroy an old red dragon without so much as a scortch...
The players had gotten to the point where they knew they could meet any challenge thrown at them, because they had the goods to kill anything they could possibly meet... until I stepped in with a standard dungeon crawl.

They were waking from one adventure to another (the main DM already had it figured out, and we were moving from the previous to the new), and ran across a small graveyard. They moved to investigate, and while they were fighting the skeletons that exploded when destroyed, and the zombies that caught fire when hit, and split open to release swarms of things, a band of orcs started firing at them from the woods.
Battles completed with the loss of a few hit points, but nothing too serious.

They searched the broken open door to the mausoleum and discovered (big surprise) a set of stairs going down. As they had most of their items in a couple of carts, and on their horses (who, decidedly would NOT go down the stairs), they had to choose what they wanted to take with them.

Along the way, they encountered a standard tough, 3 level 1ed dungeon crawl with such things as green slime, a pit trap in front of a door that was actually a mimic that fell in over top of them, a band of orcs that were part of the group from outside, rot grubs in the stack of decaying bodies, a couple of rust monsters, and all the toppings.

When they finally got back to their campsite, the character that stayed behind to watch the horses and their equipment (my character) was filled with arrows, at death's door, the horses were all dead or gone, and their precious possessions they could have used to destroy Asgard were nowhere to be found... it seems that all of these orcs were part of a very large marauding band that now had their stuff...

Things got really tense when the party was up against their own magic items, and when they didn't have the diety killers they had come to rely on during the next adventure... and the party had to start relying on themselves, and not be so cocky about things.