That something is acetate.
As much as technology has democratized the field, I think it also lowers the heights. I desperately hope I'm wrong and just old, but I haven't met someone who puts up something that they think is better. Maybe it's just because we're in the transitory phase - but digital animation has been around for decades at this point. Maybe it's Ikea versus handcrafting, and the shift is in the expected quality rather than the art elevating itself to meet priors.
That's why you animate with pencil on paper first.
Redline is a rare example where I think it's done well.
Tekkonkinkreet