I used to do:
on death of slime:
event-entity's name is "x"
Now, event-entity is not set (and it doesn't show as an error in the log) and I have to do
on death of slime:
slime's name is "x"
Skript version: 2.3.2
Use victim or attacker
if this did work at some point it shouldn't have - skript is meant to force you to use attacker or victim like @Efnilite said