ohhh... i get the question...

ok this is my closest idea...

Person A has Undead Status on them while dead, from a ring or whatever, then person B Casts Death on Person A, which makes them alive because of undead. Person A has Heal-HP reaction ability equiped and because they are now critical uses it, but because of undead status it kills them.

yah im not sure if thats right, or even if it works... If no one gets it then tell us the answer plz