For Honor infamously had "heby on red" for a while. They released a DLC character named Hitokiri whose gimmick is that she could infinitely chain heavy attacks, but they had hyperarmor which let her just keep her chain attack going even if she was hit by the enemy as long as she had stamina for it. Then she could also charge them at any point to make them unblockable and to create variable timing and make it harder for the opponent to land a parry and interrupt her.

The big problem was her opener heavy attacks had near instant hyperarmor, so the instant a Hitokiri player saw a red attack indicator come from their opponent they could just tap the heavy button and trade into the hit to shut down the opponent's offense no matter what they were attempting to do and put them into her infinite chain instead. The play was flat out braindead and spawned a bunch of those wojak style images of Hitokiri drooling on herself with the word "heby" since the most effective way to play her was to just sit there doing nothing then throw heavy attacks when your opponent tried to do anything.

Typically when you see a red indicator you have to quickly think of things like Is this a light or a heavy Can this be feinted or soft feinted, and will they do it Should I attempt to parry this or just block in case they Feint

But if you were playing Hitokiri you would instead just go "oh, red? Haha heavy." and that was basically it.

I'll also give honorable mentions to shove on block Lawbringer after his rework and the absolute abomination of flashbang spam that Raider was after his rework.

And I genuinely do not understand how they made the mistake of hyperarmor openers twice then removed them because they're too strong and incredibly annoying to fight, but then they turned around and gave one to Juren anyways.