MerakSpielman said:
Frankly, a certain level of DM "cheating" might be the only way for him to accurately role-play a creature a greater intelligence than any real-life human who has ever lived... I mean, honestly, no matter what the PCs think of, can you ever believably think that a creature with a 26 intelligence and a few centuries to plot and ponder wouldn't have thought of it already?
But remember, the party 20th level Wizard has a 26 (or even higher) Intelligence as well.
And, no amount of planning and intelligence can necessarily overcome lack of knowledge.
For example in Superman III, Superman defeated the supercomputer which could out-think and out-anticipate him by introducing a chemical which the knowledge of the computer indicated was harmless. Only someone who had actually experimented with the chemical would know that it became very unstable at high temperatures.
If as DM you state "This dragon is super intelligent and knows every single spell and every single feat and every single magic item", then yes I guess your assumption might be correct.
However, if as DM you give your players a fair chance of being successful while still maintaining a solid defense for the dragon (even if the PCs bypass that defense), which is more enjoyable for the players? Remember that the only real people involved are the players and the DM, the dragon does not really exist. Play him smart, but do not play him omnipotent. You have to give the party Wizard who also has a 26 Intelligence a fair chance of being successful.
I recently threw a juvenile black dragon against my group of 6 4th level PCs and they kicked its butt in about 3 or 4 rounds. It made the "mistake" of fighting in melee since it was too young to realize that there were actually creatures its size or smaller which could seriously harm it (it had never encountered this concept before).
The next time they meet (probably in a few more sessions), I will play the dragon much more intelligently now that it not only has had time to plan (after its close brush with death), but also has knowledge that it did not have before (namely that humanoids can seriously hurt it, especially at close range).
I see this as no different than the ancient dragon. Granted, an ancient dragon has experienced that humanoids can hurt it, but it would be the rare human who could come close to penetrating his defenses. Hence, if nobody has ever tried to coup de grace him while he is asleep, it is likely that he has not considered every possible way to do that. Sure, he might have guards and spells to protect him while asleep, but that does not mean that he would have considered every possibility to the point that the DM has to change the scenario to ensure his survival. At least, IMO. Most DMs do not let the 26 intelligence PC Wizard change which spells he brought for the day based on the scenario, why should the dragon be any different?