The Status Quo/Game Evolution/12.0
I know this horse has been beat, but with the evolution of the game and the buffing of old champs, maybe it's time to revisit some of the changes 12.0 implemented and make some tweaks. Champion specific tweaks... not mechanic tweaks.
DS - OMFG, just put him back like he was before 12.0. He would be just fine in the current meta. 7s rotation and full heals on hits.
RR - allow 100% crit rate after a combo of 15 or more. We already have crit champs and anti-crit champs. This would affect little.
IF/IIF - allow negative armor reduction
SW - she's fine. Maybe up the healing proc
OG Thor - maybe allow up to 4 armor breaks with negative armor
These aren't game breaking mechanics... hell... they're not even character buff suggestions. This is a very simple way to add relevance back to older, unused characters without having to go through the whole buff shenanigans.
We've moved well past 12.0, so its shadow shouldn't be lingering in 2019/20.