Meta-physics of an Epic Spell

[Talderas]

So I've built an epic spell, however there are some metaplanar/metaphysic issues that I still have unresolved so I'm looking for people to give ideas on how this would behave.

The spell is a Conjuration that affects a 400ft radius sphere. When cast the spell causes the plane you are currently on and the Shadow Plane to merge. We're not talking coexistent but rather both planes are present in the same area. Any creatures on the shadow plane in that area would suddenly be brought into being with the creatures from the target plane. I will call this area a bubble.

Now, this means that creatures outside the bubble on either the target plane or the shadow plane should be able to see anything inside the bubble as well as target creatures inside the bubble and move into it themselves. Everyone outside the bubble would be unaware of its existence except for the area looking visibly wrong and things leaving the bubble suddenly popping in and out of existence.

Where the spell gets tricky and what I'm trying to deterime is the effects caused by leaving the bubble. These are my questions that I'm trying to solve.

What extent should creatures inside the bubble be able to perceive creatures outside the bubble?
What happens when a creature leaves the bubble?
What happens when a creature inside the bubble tries to attack or cast a spell on a creature outside the bubble.

Opinions are encouraged.

[Radar]

I'd say that with visibility you have two options:
1. The bubble in not transparent: swirling magical energies obscure view.
2. People in the bubble see both planes mixed together with no way of distinguishing between them. People seeing through the whole bubble from the outside might see the same effect.

As for going out, I'd say the most sensible would be a coin flip to end up on one plane or the other. The same goes for attacking or casting spells.

This is epic magic: there are no hard rules out there outside the ones you impose yourself.

[Asrrin]

What you are suggesting sounds a lot like the Planar Breaching mechanics in the Planar Handbook on page 151. I'd recommend taking a look at that to see if it suits your fancy. There is even a 9th level spell on page 104, Precipitate Complete Breach, that will allow a caster to cause said breach.