When I saw the title, I immediately thought of the show "Invincible" which had abysmal animation, and lo and behold, its right there are the top of the list.
Our of curiosity why did you think Invincible had abysmal animation? Which is ironic since in the last seasons they even broke the fourth wall and did a tongue in cheek poke at their audience who criticize their animation quality explaining how they're under crunch and what techniques they use to cut corners. Quite clever actually. Didn't think they were covering up their North Korean animators though lol.
Like in one episode an alien spaceship blows up and a static gif of an alien goes spinning around.
Just compare that to the animation in Xmen '97 which has a similar episode count.