Optimization and CR

[Twilightwyrm]

I was wondering, since although I have never really done this as a DM, I have heard countless stories about it, about how much does optimizing a monster effect CR? Presumably the monsters were issued their respective CRs, in part, because of the feats they have. Since it is not difficult to imagine that an standard Ogre, or Owlbear, with Improved Initiative and Power attacked swapped in place of Weapon Focus (Greatclub) and Toughness (in the case of the Ogre), or Alertness and Track (in the case of the Owlbear) might be able to significantly more damage than their standard counterparts, it would not be unreasonable to consider them more of a challenge. So with this in mind, I was wondering, in the opinion of this forum, how much "optimizing" the spells and feats of standard monsters tends to increase their CR. So while optimizing the feats and Sorcerer spells of a Dragon could easily make it a wildly more difficult challenge than its standard counterpart, I'm thinking it would not be nearly as extreme for most monsters, and thus I am looking for analysis that is more general than specific, though specific instances are welcome.

[Quietus]

Like all things regarding CR, there is no perfect answer. In general, yes, providing something with more optimized feats could give it a CR boost - giving the Tarrasque anything other than 6x Toughness, say - the choice of feats can make a big difference. It's one thing to give Big T a bunch of feats that make his melee scarier. It's something else entirely to use feats from Magic of Incarnum and Tome of Battle to turn him into a terrifying powerhouse that isn't limited to ground-based face eating. The latter would merit a much larger CR boost than just "It does more damage!".

[Tvtyrant]

On the other hand, the Tarrasque is terribly over CR'd in the first place.

But yeah, taking a T-Rex and adding Iron Heart Surge would make it much tougher (whats that, you can't disable it anymore?)

[Biffoniacus_Furiou]

It depends on the optimization level of your PCs. If your players tend to make strong, optimized characters, then it's fair to give opponents more optimal feats, spells, etc. in place of what a typical specimen would have. You don't need to increase their CR unless you also give them the elite array of ability scores, increased HD or class levels, or one or more templates.

One example of an easy way to optimize a creature with just feats is to give a Hydra the feats Snatch, Improved Snatch, and Multisnatch, most of which is in the Draconomicon. That way it can grab a medium or smaller opponent with each bite, and just the head that grabbed them will be considered grappled. Each round after it can make bite attacks against grabbed opponents with other heads as though from outside the grapple, so they won't get any Dex or dodge bonuses to AC. Put it in a murky underwater tunnel that the PCs have to swim through to reach their destination, so they'll be at risk of drowning as well while they fight it.