In ‘Marvel Studios’ Assembled: The Making of Agatha All Along, ‘Aubrey Plaza talked about playing Death, explaining that she enjoyed the character’s complexity and contradictions.
She appreciated being able to play three different versions of the same character, which she felt could work well in the MCU due to her otherworldly and yet grounded nature.
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Deadpool is quasi immortal so far. The curse takes it to full immortality where he can never die.
The difference is not aging instead of aging very slowly and he can be nearly obliterated and still come back from nothing but a single cell, so a vial of his blood kept safe would allow him to regenerate compared to needing a chunk intact, ideally brain matter.
They could bring Thanos back in the Deadpool Universe because it isn’t stated that Thanos was killed in that Universe.