Last patch's adjustment last patch ended up a very slight nerf (less than .5%) for both top and support. So we're making some support-focused improvements to compensate.
As a champ in both Top and Support, Tahm Kench requires periodic maintenance as the meta shifts to ensure both roles of his roles are equally supported. In this case, Dusk and Dawn's addition to the game this season has shifted this balance in favor of top lane, so we’re adjusting how his passive scales to help balance him out.