The franchise died when The Marionette stopped being relevant. Ignoring the FNAF 1 animatronics, The Marionette is the most "FNaF" character from them all.
>His own music box mechanic parallels Freddy's toreador march when the power is out
>Amazing character design, it stands out the most to every other character, including modern ones. As he doesn't appear to be a robot.
>His expressionless face can subtly express emotion depending of the camera angle, meaning that creative around camera shots are necessary to properly animate him
>Biggest connection to many spirits and his character role combines with everyone. He's the ringmaster of the missing children, Springtrap's nemesis, Elizabeth's opposite moral reflection, Mimic is related to Nightmarionne
>Even more paranormal than Golden Freddy, as he behaves more demonic and even organic. He can actually extend, expand and regenerate limbs like a tentacle venom mess in the books. This breaks every established remnant and spirit rule in the franchise, who not even Golden Freddy went as far as that. And this remains entirely unexplained.
Even if his concept was not executed as it deserved, Lefty was single-handedly making Pizzeria Simulator a FNaF game. Springtrap evolved into being a Slasher, just like Sans got his own fandom apart of Undertale. Baby and Mimic are a completely different game genre.
FNaF died when the Puppet burned.