2 small changes for Deathfire
Ok, I still don't know why after all this time Riot hasn't updated this mastery, I understand it got to be toxic with Dot's but now it is controlled and it hasn't broken those ap dot champs as it did in the past. Also Deathfire is one of those masteries that I recognize to be good but that doesn't feel rewarding or thematic and fails at some specific points: lets check.
*Deathfire is a theme, yet it fails to accomplish it, it just feels like a trail a dust that tickles the skin of the enemy (I know it isnt that way, yet it feels that way).
*For Deathfire to deal the same damage that Thunderlord does you usually require at least 7 to 10 seconds of constant ticks of this mastery.
*Some people say that Deathfire is good for AoE and Thunderlord is not, yet Thunderlord deals AoE damage (and I have made some kills for proximity due to that damage).
*While it is wise for Deathfire to have such a reduced effect on DoTs, it fails for most mages and many champs as it only lasts for 2 seconds on AoE abilities (most abilities are AoE).
*Thunderlord adds 10 damage for each level (180) , while Deathfire not even 1, it is 0 for Deathfire (remains at 8).
*Thunderlord reduces its cooldown per level and is quite fairly easy to proc in a rotation, thus this makes it's dps increase both with level and items, making the efficient range for Deathfire to reach the DPS of Thunderlord really hard, specially when it grows with items and not with Level, usually you would need at least 600 AP to reach the damage capacity of Thunderlord on 6 seconds of Ticks.
*The damage of Thunderlord is instant, it bursts you and there is no counter for it, when you are bursted you can't react, you cant heal yourself if you die too quickly, you can't ask an ally for help cause you died, you can't use an sneaky Zonyah if you didn't reacted on time, or a Mikael, or a Locket, or any shield, or simply life steal a bunch of minions.
*Since it doesn't add burst to your damage it might actually expose you, since it allows the enemy to have a little bit more time to react to you, so in situations where thunderlord would have saved your ass, Deathfire got you killed.
*Since Thunderlord is instant you can easily see the damage it deals, but Deathfire is divided into 2 ticks per second, all of them really small, you can't see the total damage it deals quite well, therefore it doesn't feel rewarding.
As you see there is a difference between feeling something is useful and it really being useful, right now deathfire IS useful, but it doesnt FEEL that way.
Suggestions:
WARNING: this are changes I'm suggesthing, therefore I am saying TEST them, I don't want them introduced in to the game too quickly because I don't want to see this mastery broken to the skies, specially I don't want to see it broken to the skies on the live servers. Anyways these changes are small, I don't want it to get too much adventage.
*Make Deathfire proc for 3 seconds on AoE abilities; why? because most of it's users are gonna proc it on AoE abilities, also, let me remind you it requires at least 7 to 10 seconds for it to match Thunderlord, and in that duration Thunderlord has already reseted it's cooldown on the lategame, for an AoE mage to do so you would have to cast AND hit your enemies once each 2 seconds, which is a lie, almost no mage has that poke capacity and if a mage gets you in his range he is gonna use all his combo so quick and yet the duration of Deathfire will be the same. If the duration of Deathfire were to be increased by stacking time when landing abilities on your enemies then it would make sense for it to only have 2 seconds on AoE abilities, yet it doesn't and it fails for many mages for that reason.
*Which are those situations where you feel Deathfire is most rewarding? when do you say "lol that is so sweet"?; when the enemy runs away low in life and Deathfire kills it, even through it is somehow rare when it happens it feels really good, in order to make this moments more common I want to ask one thing; make Deathfire deal 50% or 100% bonus damage to targets below 10% (or 6%?) of their max life. I know some of you might say that this is too much, but let me ask you something, if you are on a fight or if a poke ability got to hit you and you were left so low in life and in top of all of that you have a dooming debuff called DEATHFIRE all over your body burning you to the core.. do you believe you deserve to live? do you believe it feels thematic that you scape so easily when you did nothing to save yourself?... ah and let me remind you, there is time to save yourself; you have time to use any of these 
or any heal of your preference, there is a lot of time for you to react, yet as a Deathfire user this ones are the moments that feel more thematic and rewarding to me, and I want more of them.
#Anyways, tell me what you think, and remember, I am saying TEST, not ADD. I want to see how it goes on the PBE, I don't want another broken thing haunting me on the Live Servers, I think we all have enough of these things.
Ah, also, a 
for you.