I've been wondering about this ability/mastery combo.
Does Deathfire Touch get procced ONCE on the cast of MF/Luc ult? If so, does it proc on everyone that gets hit or (like a sheen proc) the first person to be hit?
Or does Deathfire Touch get procced every time it hits something, without limit?
My understanding is that every instance of damage will proc it (for the two ults you mentioned, at half strength, since they are AoE). Each proc will renew the duration to 3 seconds (1.5 seconds for AoE), rather than stack damage. It will proc on every target affected, not just the first one.
Multiple instances of damage will refresh the duration of deathfire touch but not stack. It can be applied to multiple enemy champions, but area of effect and damage over time abilities apply 3 (+ 25% bonus AD) (+ 10% AP) magic damage over 1.5 seconds instead.
It definitely won't stack, but it would get its duration refreshed, but it might only proc once every 2-3 secs depending on its cooldown. (if it has one)
