Well, I'm in the middle of planning out the third adventure, and for a cap-stone fight, I want to pit my four PCs (all third level) against a pair of Rage Drakes and a little over a dozen Needlefang Drake minions. Consider that they will have gone through five to seven other encounters roughly equal to their power level.
Does this seem like it will be too hard for a group comprised of every character role? Or would they have a chance?
BUT,
If they are having trouble then it would not be fair game.
just to inform you a single day of encounters should be 4-6 encounters of standard encounters (encounters their level), a hard encounter (2-4 levels higher) counts for 2 encounters if done right.
Now I have seen a party go though 9 encounters in one day but they were tapped out, they even ran from a group of kobolds 2 levels lower than them!
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to make this Semi-short and sweet...
STAY FLEXIBLE! if they have used their dailies before the fight and are low on healing then maybe tone it down a little, replace one rage drake with 2-4 minions or add one more swarm.... but if they are having trouble to get to that point its better to let them have a smaller fight than seems tougher than to kill them all because you had a huge boss fight planned.
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If it was me I would only put them against 4-5 encounters then a boss, but I might take away 1 enounter if they were having problems.
Hope that helps
Tis the season to be Gaming
GG