I already know the antimagic field suppresses the usage of the supernatural abilities, but i want to know what happens to some effects like an alternate form when using change shape or supernatural invisibility.
If a creature that used the ability enters the antimagic field, what happens?
Does a kitsune with the fox shape feat, in fox shape, revert to fox folk form or remains restrained to the fox form inside the antimagic field?
Does a sprite with supernatural invisibility becomes visible or does she remain invisible and cannot become visible inside the antimagic field?
Does a titan with change shape in human form revert to titan?
The downside of assuming they don't lose the alternate form or become visible is that makes the su overpowered.
The downside of assuming they lose the alternate form and become visible is detect magic will detect such creatures with ease, making those su underpowered.
Best Answer
Yes
Because as long as the effect has a duration and is magical, it will stop working inside an antimagic zone. And once you walk out of it (or the zone walks away) the magical effects return.
Some spell effects, like flesh to stone, have no duration, are instantaneous effects (see bellow), which are not subject to antimagic zone because the spell already happened and what remains is the result of the spell.
The "stone" is not magical, its real.
Another example is the damage caused by a Fireball. The spell itself wouldnt work inside an antimagic zone, but the damage caused is instantaneous, once the spell is cast and the damage is taken, the remaining effects (health lost, burn wounds, ego hurt, etc) are not magical per se.
Shapechanging in general mimic the spells from the polymorph school, which do have a duration.
Change Shape (From universal monster rules) says: This ability functions as a Polymorph spell, which has Duration 1 min/level (D).
But Change Shape specifically clears it up that the creature can remain in that form indefinitely unless said otherwise. Meaning that it has a long-lasting duration.
Called creatures won't get dispelled either, because the spell that bought them to the material plane already did it's work, the creature is physically here and won't disapear in an antimagic zone. But a summoned creature will disapear as long as it remains "inside" the zone.
Subquestions
The effect is on the creature? Or it was just the caster? The person with the active effect (it has duration left, even if undefined) will get surppressed.
Yes, because her fox shape is a polymorph effect with a duration.
Yes, she will become visible and won't be able to turn invisible again. The same will happen to an invisible stalker, they will show up as a ghostly vaguely-humanoid creature with no details (the picture we see in the bestiary), but they are no longer invisible.
Yes, because change shape is a magical effect that has a duration.