Use your Illusion....

[Jimlock]

There are conditions that let you see through them automatically. One, of course, is making your Save. Another is physical contact that it fails to react to appropriately.

RC:

ILLUSION
Illusion spells deceive the senses or minds of others. They cause people to see what isn’t there, not see what is there, hear phantom noises, or remember events that
never happened.
Saving Throws and Illusions (Disbelief):
Creatures encountering an illusion usually don’t receive saving throws to recognize it as illusory until they study it carefully or inter- act with it in some fashion. A successful saving throw against an illusion reveals it to be false, but a figment or phantasm remains as a translucent outline. A failed saving throw indi- cates that a creature fails to notice something is amiss. A creature faced with proof that an illusion isn’t real needs no saving throw. If any viewer successfully disbelieves an il- lusion and communicates this fact to others, each informed viewer can make a new saving throw with
a +4 bonus.
Figment
A figment spell creates a false sensation. Those who perceive the figment perceive the same thing, not their own slightly dif- ferent versions of the figment. Figments can’t make something seem to be something else. A figment that includes audible effects can’t dupli- cate intelligible speech unless the spell’s description specifically says it can. If in- telligible speech is possible, it must be in a language you can speak. If you try to duplicate a language you can’t speak, the fig- ment produces gibberish. Likewise, you can’t make a visual copy of something unless you know
what it looks like. Because figments and glamers are unreal,
they can’t produce real effects the way that other types of illusions can. They can’t cause damage to objects or creatures, support weight, supply nutrition, or provide protection from the elements. Consequently, these spells are useful for confounding or delaying foes but use-
less for attacking opponents directly. A figment’s AC is equal to 10 + its size modifier.
Glamer
A glamer spell changes a subject’s sensory qualities, making it look, feel, taste, smell, or sound like something else, or even seem to disappear.
Pattern
Like a figment, a pattern spell creates an image that others can see, but a pattern also affects the minds of those who see it or are caught in it. All patterns are mind-affecting spells.
Phantasm
A phantasm spell creates a mental image that usually only the caster and the subject (or subjects) of the spell can per- ceive. This impression is totally in the minds of the subjects, not a fake picture or something
that they actually sense. It’s a personalized mental impression. Third parties view- ing or studying the scene don’t notice the phantasm. All phantasms are mind- affecting spells.
Shadow
A shadow spell creates something that is partial- ly real. Such illusions can have real effects. Damage dealt by a shad- ow illusion is real.

all questions answered... Rules Comp. Rules!

 

[Theo R Cwithin]

And going one step further, I seem to remember reading somewhere that you can always choose to fail any saving throw.

Found it, under Spell Descriptions:

Voluntarily Giving up a Saving Throw

A creature can voluntarily forego a saving throw and willingly accept a spell’s result. Even a character with a special resistance to magic can suppress this quality.

 

[Visigani]

If this is specifically about Illusion(Shadow) spells (eg, shadow conjuration), then, yeah, I'd think a believer could ride the shadow "horse", if only because the shadow creature is actually made of stuff summoned from Somewhere Shadowy, stuff that can even affect disbelievers on occasion.

...Which is why, just for giggles, I might even allow a disbeliever to (try to) ride such a "horse"-- except that he'd have to beat the % chance to interact each round, or else fall off (or, more precisely, "fall through").

As for willful disbelief, I'm not so sure. I don't see that it's terribly problematic to allow it, at least for the caster. If it's an issue, maybe make the caster make a DC15 Will save against his own grasp on reality; if he fails, he has to make a a Will save as normal to disbelieve; if he succeeds, he can choose his delusions freely and can "Take 1" on the Will save to disbelieve.

you gotta believe, man... YOU GOTTA BELIEVE!!!!!!

 

[StreamOfTheSky]

you gotta believe, man... YOU GOTTA BELIEVE!!!!!!

Indeed! Reminds me of my Cleric / Shadowcraft Mage, who worshipped that campaign's god of shadows. He purposely failed his save for his shadow (greater) mage armor. It gave full protection because he believed in it. Literal faith armor!

 

[Empirate]

I'd say if you play a Wizard who's into casting illusion spells, you'll have to assume the following:

1. Your PC is very, very intelligent, quite likely more intelligent than any of us here. His/her mind is capable of things we literally haven't dreamed of. Any of you know The Name of the Wind? If you think about what a Wizard PC is capable of, think Kvothe.

1. a) In the case of Sorcerers, Bards etc., they just have personalities so forceful that it provides them with A LOT of sheer, raw willpower - which basically can do the same things in D&Dland.


2. The PC in question is likely very advanced in cognitive sciences (such as they are in a medieval fantasy world), and the philosophy of aesthetics. He/she likely believes in the power of the mind to shape the world. Like a constructivist, but EVEN MORE.

3. The PC in question would likely be able to admit that his horse isn't real in the same sense as a stone found by the road is real or his/her own nose is real. However, he/she'd be able to come up with one hell of a convincing argument how that really makes no difference in the grand scheme of what reality is all about. He/she'd be able to believe the horse is real and isn't real, at the same time. "Is beauty real? Is justice real? Is friendship real? No, they're not, not like a stone is, it's all in our heads - but of course, they ARE real, in a very tangible sense, AS WELL. Why not extend that concept to a horse? All a matter of perspective..."

4. Also, the PC in question knows that the horse is at least 20% objectively (whatever that means) real. "We can work with that, it's all a matter of extrapolation! If I 20% don't fall through the saddle, I only need to know why that is, and apply it to the other 80%! Of course, that's easier said than done..."


So what it all boils down to, IMO, is that casters know their spells, they know just how they work, they know what they're capable of etc., on a very fundamental level. So why shouldn't a caster be able to abuse the capabilities of a Shadow Conjured Phantom Steed spell?

 

[Whizbang Dustyboots]

Shadow stuff is partially real. The only reason I'd argue against the caster riding one conjured this way is that it arguably negates the need for the Phantom Steed spell.

 

[Whizbang Dustyboots]

So why shouldn't a caster be able to abuse the capabilities of a Shadow Conjured Phantom Steed spell?

As long as it was a properly nerfed version of the Phantom Steed (as is standard for Shadow Conjurations), it seems to fit with the intent of the rules, IMO.