A bad support champion is one that provides very little utility to the team. What a team needs can change from game to game so here are five supports in League of Legends Patch 8.12 that provide almost nothing to their team, regardless of the circumstances.
Taric is in an alright spot as a mid laner right now but has one of the lower support winrates and should suffer from the Patch 8.12 changes. His lane phase is somewhat weaker than most other supports and relies heavily on landing his stun which is an easy ability to dodge on account of how telegraphed it is.
Taric is a champion that benefits from Ardent Censor so that nerf should hurt him slightly.
Although Ivern's shield was untouched in the shield duration nerfs, his support itemization was hit pretty hard. As a champion that loves to rush Athene's Unholy Grain and Redemption, he will no longer have the shielding power he once did, even if he is great at taking the Rift Scuttler.
Karma had already been sliding in terms of win rate as a support pick and will be even worse in Patch 8.12 after the shield duration nerf and the nerf to Ardent Censor and Redemption. Although her early game should still provide a fair amount of pressure, Karma can no longer rely on massive mid game Ardent Censor empowered shields because they won't last as long or provide nearly as much for the team.
Lulu is in the same boat as Karma but is getting hit a bit harder by the shield duration nerf since her shield from Help, Pix! was longer than Karma's before the nerf. Obviously she will also suffer from the item nerfs and should be de-prioritized during Patch 8.12.
1. Tahm Kench
Tahm Kench has the ability to provide insane amounts of utility to his team but that utility is very circumstantial. For example Devour, his W, is a great ability for getting out of long duration stuns. The key is that there needs to be a long duration stun on the enemy team otherwise Devour doesn't provide the same value.
Without champions like Ashe or Malzahar around anymore to take advantage of, there are precious few abilities that Tahm Kench actually counters and therefore will continue to have one of the lowest support win rates.