Can I use Eternal Mask on a vampire that has was killed while it
represented a Spell of Life mummy?
Spell of Life
+1 stealth action. Put this card in play. Only one spell of Life may
be played each turn. You may burn five Spells of Life to put up to
five vampires from your uncontrolled region in play. Each represents a
unique mummy ally with life equal to capacity, 1 bleed and 2 strength
who can enter combat with a minion as a (D) action.
Eternal Mask
+1 stealth action.
[ser] (D) Bleed at +1 bleed.
[SER] Put this card on this vampire and move a unique vampire from any
ash heap to your ready region with any amount of blood from this
acting vampire. The minion with this card cannot take actions, block,
play reaction cards or vote. You may burn this card and the chosen
vampire during any untap phase.
Correct.
> Can I use Eternal Mask on a vampire that was killed while it
> represented a Spell of Life mummy?
Yes. Eternal Mask doesn't look at how the vampire card came to be in the ash heap.