Slaking is special because it has a gimmick: the BST of a legendary Pokémon, but horribly detrimental Ability.
This could also be true for Dipplin 2: the Squeakquel.
I thought this one made sense.
Ninjask'd by
woodgoldtwo, Duraludon's SpA is 120.
That said, this statline stinks. Speed taking a hit is one thing, that's not uncommon among evolutions, but none of the other stats increase much.
Going from a BST of 535 to a presumed 555 sucks. For context, there's a BST increase of 50 when Rhydon evolves into Rhyperior, and when Scyther evolves into Scizor, at least the Atk and bulk increase was visible despite an identical BST.