OoC thread

[GM Marvel]

If I was DM, I feel it would work until the moment an arrow or some such struck it the first time and sank right through.  Figments tend to be disbelieve-able.

I agree.  As soon as someone interacts with the illusion which includes attacking or studying it, they would get a save throw disbelieve.  As soon as they disbelieve they know the Figment is fake and can see a faint outline of the illusion.  But if they have proof the illusion is false like falling through an illusionary floor, the save is automatic.

From pages 173-174 of the Player's Handbook:

Saving Throws and Illusions (Disbelief ): Creatures encountering an illusion usually do not receive saving throws to recognize it as illusory until they study it carefully or interact with it in some fashion. For example, if a party encounters a section of illusory floor, the character in the lead would receive a saving throw if she stopped and studied the floor or if she probed the floor.

A successful saving throw against an illusion reveals it to be false, but a figment or phantasm remains as a translucent outline. For example, a character making a successful saving throw against a figment of an illusory section of floor knows the "floor" isn't safe to walk on and can see what lies below (light permitting), but he or she can still note where the figment lies.

A failed saving throw indicates that a character fails to notice something is amiss. A character faced with proof that an illusion isn't real needs no saving throw. A character who falls through a section of illusory floor into a pit knows something is amiss, as does one who spends a few rounds poking at the same illusion. If any viewer successfully disbelieves an illusion and communicates this fact to others, each such viewer gains a saving throw with a +4 bonus.

From Rules of the Game: All about Illusions

If you make a successful saving throw against an illusion effect and disbelieve it, you stop perceiving the illusion and it has no effect on you at all. Illusions from the figment or glamer subschools, however, remain behind as faint, translucent outlines even after you successfully disbelieve them. These see-through remnants have no effects on you at all, but serve to remind you that the illusion is there. It also reminds you of those things with which other less perceptive individuals might have to deal. The rules use an illusory section of floor (presumably a figment) as an example. If you have disbelieved the illusion, you see the floor (light permitting) as it is; that is, with a gaping hole in it. You also see the outlines of the illusion, however, which can prove handy when an unsuspecting ally comes on the scene. 
The rules don't say what happens if you successfully disbelieve a figment or glamer that doesn't have a visual element. It's a safe bet, however, that you remain aware of the figment or glamer without being affected or hindered in any way.