At this point, I'm not convinced you even have one. I'm pretty sure you're throwing darts at a dart board to decide what is going to be changed, then subsequently rolling dice to decide how hard they're buffed and nerfed, etc.

Aftershock is already OP, at 20+30% bonus armor/mr. Beginning with 8.2, it is getting a BUFF, to become 85-175 flat armor/mr, reducing it's base damage and health ratio slightly, while adding a small (10% and 15% respectively) ad and ap ratio to it. First off, a full tank mastery doesn't need damage ratios from AD and AP, let's get that out of the ay right there.

Second, let's take a look at the defensive stats, which are procced on any cc whatsoever. On many bruisers, it is currently largely unusable, for obvious reasons (It's percent armor and mr). After 8.2 hits, any self respecting bruiser with one small cc like xin zhao third q, for instance, can build full damage and still ahve 250 armor/mr for 3 full seconds, then have their xin zhao ulti for several seconds after that. Yikes.

The real problem is when you start to look at non-tank and even non-bruiser roles. When you have 175 FLAT armor and mr flying around on any cc, you risk giving a late game tristana 175 flat armor and magic resist in addition to what they may have built added to their base stats. Tristana R, Vayne E, Varus R, Draven E, Ashe R, Cait W, etc. all proc aftershock.

That would be some really crappy stuff to see, but let's think about what else procs aftershock....

Veigar E, Sydnra E, Orianna R, Aurelion sol Q/R, Azir R, Lux Q ... We'll leave it at that, but we could come up with more.

Who here is excited for the 250 armor, 1500 ap veigar walking around... No one.

But back to what they were really intending to work on... the base damage of aftershock is being nerfed by 20 at all levels, along with 0.5% max health damage taken away from aftershock as well. Which means, after resistances, aftershock is going to hit ADC's (if they're still in range for the explosion, even) for about 20 less damage early in the game. Yet, if the aftershock-user is attacked even twice, which is reasonable in fights while running away from some cc support that you don't want on your face (because you're not going to attack the enemy adc when you have a leona slapping you silly, you're goign to attack move away), you are going to deal much more than 30 less damage to the aftershock-user.

This means that although the damage is nerfed, the amount of damage you deal will be further nerfed.

Aftershock is already broken. Please, for the love of all that is holy, stop :)