Can Sett's legend ability be activated to prevent a unit from being killed by Cull the Weak when all opponent units are buffed?

Ruling: Yes, Sett's legend ability can be activated in response to Cull the Weak. The opponent still chooses one of their units to be killed, but then spends the buff on that unit to replace its death with a recall instead.

Sequence:

• Cull the Weak is played
• Opponent chooses one of their units
• When that unit would be killed, Sett's ability activates
• The buff is spent on that unit
• The death is replaced with a recall