When a swarmmonger's fecund familiar becomes a swarm, what qualities does it retain?

[Marcella]

The book reads, "While in swarm form, the familiar loses the improved evasion, share spells, deliver touch attack, and scry on familiar special abilities. It uses its normal AC, saving throws, and skill bonuses, and it gains the swarm subtype and the ability to make swarm attacks ..."

1) If I use "share spells" to cast longstrider upon my cat familiar, Felix, and Felix then bursts into a swarm, does the spell still work for the cat swarm? If not, does Felix still have the spell active after reverting back into a single cat?

2) If I cast "mage armor" (not a self-only spell) onto Felix, will the subsequent swarm benefit from the AC bonus?

3) What happens after a foe reduces the swarm to 0 hit points? Does the swarm dissipate, leaving a single unconscious cat familiar? Or is Felix dead, or conscious?

4) If I instead use Shelob the scarlet spider familiar, does the swarm gain the familiar's poison ability in its swarm ability?

5) If Felix is standing next to a foe, and he then bursts into a swarm that encompasses the foe's square, does the foe get an AoO?

Thank you!

[Boldston]

I have a swarm monger character that I use in PFS, and I initially had all the same questions you are asking. After much review of the rules these were the conclusions I reached and play by:

1. Share spells allows you to cast spells upon your familiar that you would normally not be able to. When your familiar is is swarm form you "lose" share spells, which I interpret to mean the spell would end.

2. Mage armor is a creature targeted touch spell, so it would stay with your familiar when in swarm form. However, in swarm form you gain the swarm subtype which states that "A swarm is immune to any spell or effect that targets a specific number of creatures". So the spell is still on you, you are just immune to its effects (translation lose the benefit). When you revert you familiar back to normal, the spell is still there and you once again gain the effects.

3. Swarms are not killed, the bestiary says the following: "Reducing a swarm to 0 hit points or less causes it to break up" and "Swarms are never staggered or reduced to a dying state by damage" A dying creature must have negative hit points. To me this means that when your familiar is reduced to zero hit points (it can't go negative), it breaks up with a few copies of itself wondering around and it is basically nonfunctional. But you still can revert it back to normal and heal it.

4. Yes. Swarm is a subtype. The spider still has its vermain traits in addition to swarm traits. Since a spider damages by bite, the swarm has poison and can also overcome Piercing / slashing / bludgeoning DR.

5. Yes, whether the swarm bursts into the foe's square or moves in normally, the familiar is still entering the foe's square.