Death Spells and Advantage Interactions.
 

Underworld Imprisonment (And also Rift to Hell) and Jumper
If you have Jumper (Spirit) or maybe Jumper (Interplanar) can you just return with a successful IQ roll?

Aggravated Injury and Unkillable 1, 2 or 3.
Does Aggravated Injury Afflict (Negate Unkillable 3)? If not, how does it interact with Unkillable 1, 2 or 3?

Would it be fair to say that to those who have some level of Unkillable, the first level of Aggravated Injury means:
If you have Unkillable 1 Aggravated Injury can kill you if it does does 2xHP, but you still get to roll HT to Survive. If it does 3xHP you roll HT twice needing to succceed on both rolls, 4xHP you roll HT 3 times, 5xHP you roll HT 4 times, and 6xHP you die.
If you have Unkillable 2 Aggravated Injury can kill you if it does does 11xHP.
If you have Unkillable 3 Aggravated Injury can't kill you.

The second level of Aggravated Injury means:
If you have Unkillable 1 Aggravated Injury kills you if it does does 2xHP, no HT roll to survive.
If you have Unkillable 2 Aggravated Injury Aggravated Injury can kill you if it does does 2xHP, but you still get to roll HT to Survive. If it does 3xHP you roll HT twice needing to succeed on both rolls, 4xHP you roll HT 3 times, 5xHP you roll HT 4 times, and 6xHP you die.
If you have Unkillable 3 Aggravated Injury can kill you if it does does 11xHP.

Does that seem fair?

Re: Death Spells and Advantage Interactions.
 

You'd have to check with Kromm to be sure, but I'd say it might be possible only with the Rift To Hell spell. The newer spell's intent seems to preclude easy escape under your own power that way.

Re: Death Spells and Advantage Interactions.
 

I wouldn't say requiring a 100 point advantage qualifies as "easy escape".

Re: Death Spells and Advantage Interactions.
 

*shrug* You were the one who postulated Jumper's availability. The easy part is using it if you have it. LIS, a reading of the spell makes me think that just having Jumper (or knowing Plane Shift yourself) isn't enough to escape UI. There needs to be some sort of negotiation with TPTB.

INK

Re: Death Spells and Advantage Interactions.
 

Underworld Imprisonment doesn't just teleport the victim to the Realm of the Dead or Hell or wherever . . . it also registers the subject as dead, strips soul from body, and puts the soul in the custody of a god of the afterlife. The spell name includes "imprisonment" for good reason! Summoning the subject back explicitly does not work, and the same goes for tricks such as Jumper; negotiation with the The Powers That Be is expressly required. That said, extradimensional entities that weren't alive to begin with may well not be "processed" the same way (the spell implies as much), so for them, Jumper might work. What markers qualify a being for such status necessarily vary by campaign, and could include expensive advantages (such as the Spirit meta-trait), mere features, or even disadvantages (such as Social Stigma (Dead)).

As for Unkillable, note that none of these spells kill by taking the victim to -5×HP or -10×HP. They inflict a -50- or -100-point disadvantage that causes death to occur without a HT roll at -1×HP or even 0 HP. The fairest way to handle this would be to say that the disadvantage inflicted reduces Unkillable point-for-point. What happens next would depends on the quantity of injury (real or virtual) the spell inflicts.

A death spell that normally insta-kills at -HP inflicts a -50-point disadvantage, so . . .

. . . Unkillable 1 [50] effectively goes to 0 points. If the victim is reduced to -HP, he might die like anyone at -HP or worse. Make the usual HT roll(s) for this. If the spell happens to reduce the subject to -5×HP, then don't bother with a HT roll; death occurs.

. . . Unkillable 2 [100] effectively goes to 50 points, so treat it as Unkillable 1. Being at -HP simply can't kill the victim. If the spell happens to reduce the subject to -10×HP, death occurs without a HT roll.

. . . Unkillable 3 [150] effectively goes to 100 points, so treat it as Unkillable 2. Being at -HP simply can't kill the victim. If the spell happens to reduce the subject to -10×HP, death occurs without a HT roll but the subject's body will grow back eventually, if this isn't prevented.

A death spell that normally insta-kills at 0 HP inflicts a -100-point disadvantage, so . . .

. . . Unkillable 1 [50] effectively goes to -50 points, so treat this as a regular case of Fragile (Unnatural). If the victim is reduced to -HP or worse, he dies without a HT roll. In effect, the spell works like one that kills at -HP, not at 0 HP.

. . . Unkillable 2 [100] effectively goes to 0 points. If the victim is reduced to -HP, he might die like anyone at -HP or worse. Make the usual HT roll(s) for this. If the spell happens to reduce the subject to -5×HP, then don't bother with a HT roll; death occurs.

. . . Unkillable 3 [150] effectively goes to 50 points, so treat it as Unkillable 1. Being at -HP simply can't kill the victim. If the spell happens to reduce the subject to -10×HP, death occurs without a HT roll.

Thus, Unkillable is a reasonably good defense against death (as it should be), but not a guarantee.