Mustrum_Ridcully said:
A immensive host of abilities of monster abilities are too powerful to be described simply as a feat. You can jump through hoops and add prerequisites that make it next to impossible to take them before a very high level. But monsters have access to them a lot earlier.
That's a feature, not a bug. The system is working as intended - extremely powerful abilities should be very difficult to get. And all of the abilities you described are available to PCs in some form, be it other types of damage reduction from class features or magic items, teleport or anti-magic abilities from spells, or whatever. The specifics are different (particularly the "at will" nature of the teleport ability), but those abilities are available.
(at which point you will always be able to point to a Wizard or Cleric that can use the ability a few times per day)
The underlying weakness of 3e that this uncovers is that no-one did a formal analysis of the available powers and determine at what levels they are appropriate, and how frequently.
Fly is a 3rd level spell because it always has been, and it always has been because whoever added it to the game decided that that "felt right". Never mind that the ability to fly fundamentally changes the nature of a huge range of encounters. Never mind that it
also makes a big difference whether it is in the hands of a Wizard (who may or may not have it prepared, probably has only one copy prepared, and had other 3rd level spells to choose from) or a Sorcerer (who if he has it at all can probably be assumed to by flying in every encounter).
That is the work that should be done. Assign levels to every power, and note how those level vary depending on whether the effect is one-use/frequent-use/at-will. Then, in your monster-design guidelines note that monsters buy these things always as though they are one-use effects, because the typical monster will only appear in a single encounter. IN theory, PCs will also be able to get those powers (via feats, spells, magic items, class features, or whatever), but they're going to pay a premium for them.