[Powers] Triggering Alternate Form Upon "Death"

[JCurwen3]

How would you build this? A character that, upon dying in their base form, they actually don't die, but switch to a more powerful Alternate Form? In that form if they're killed, they really do die. The idea is that the "dead" base form heals (from death) completely (or nearly so) on transformation to the alternate form, but then while in that form the damage is reciprocal to the base form. The "upon-death" form is always healing when dormant. The character can't enter the other form without first dying, although they can kill themselves (with a Will roll, penalized depending on how) to do this. A lot of this is balanced by the alternate form having serious mental disadvantages, including Berserk (6).

Can death (failed HT roll to stay alive or -5*HP automatic death for most characters, or -10*HP Unkillable characters) be a valid (Uncontrollable) Trigger for the switch to an Alternate Form?

I thought that the forms would have Non-Reciprocal Damage and Reciprocal Rest, but that isn't exactly what I want. I'd more want something like Extreme Regeneration to switch on to heal the base form upon the transformation, and then for the damage to be reciprocal to the base form while in the alternate, with damage to the base form never affecting the alternate form.

Does the base form need some kind of limited, modified Unkillable for this to work? It needs to be as fragile as if they didn't have that trait (can fail normal HT death checks, automatic at -5*HP). But on the other hand if it really dies then can the character by RAW stay alive to switch to an Alternate Form, and then have the dead base form heal?

I hope that all makes sense. Really not sure how to build this.