Exactly when does someone get a Reflex save? And, for that matter, when is someone denied one? Do you have to have some sort of cover? If you don't have cover, do you get one?
This question keeps coming up in my campaign, and I just wanted to know if anyone had any thoughts or official rulings on this.
Squid
You get a reflex saving throw every time that the spell (or supernatural or exceptional ability) says it does.
All saving throws reflect the ability to avoid unwanted effects of some type, and a saving throw is always allowed, unless the spell (or supernatural or exceptional ability) specifically says otherwise... such as magic missile.
Even if a person is bound, tied to the stake, immobilized, with no cover, and soaked in oil... you still get a reflex save against fireball or a dragon's breath weapon.
It is easy to imagine a peson jumping, twisting, and leaning out of the way of some area effect and come out unscathed... and sometimes that's exactly what happens. But not always. Sometime's it is simply the muscle movement inside the body that provides enough "give" that reduces the impact on the individual.
I have seen martial artist take hits to the stomach and not move a single inch... but also didn't seem to get hurt at all. He knew how and when to tighten and relax certain muscle groups to "roll with the punch," but without rolling.
Now... moving onto Will saves.
Let's say you charm a person, roll some perfect diplomacy, bluff and charisma checks to absolutely convince him that you are about to cast Cure Light Wounds, but instead you cast Phantasmal Killer.
That person still gets a Will save, followed by a Fort save, as per the spell description. You can fool a person... but you can't fool it's automatic responses. The person would recognize that something "bad" is happening, and will get the chance for the appropriate saving throw.
Big Jake is essentially correct. You can voluntarily fail your saving throw, but you are never denied a saving throw if the spell calls for one. However there are a few conditions that can affect your chances for success, especially on reflex saves. Here are a couple of examples from the SRD:
"Cover and Reflex Saves: Cover grants you a +2 bonus on Reflex saves against attacks that originate or burst out from a point on the other side of the cover from you. Note that spread effects can extend around corners and thus negate this cover bonus."
"Helpless: A helpless character is paralyzed, held, bound, sleeping, unconscious, or otherwise completely at an opponent’s mercy. A helpless target is treated as having a Dexterity of 0 (–5 modifier)."
Since your reflex saves are modified by your Dexterity, a helpless character would take a penalty to his reflex saves.