MISSING DATA:
There are no specific details (obtainable from the '/dt cotton down' command line) regarding to what degree Cotton Down affects speed.
I get that we're waiting on Bulbapedia and Serebii to copy each other before we copy them (which is lazy imo) but it would be nice to know in the meantime, if we know and nobody has formally written it.
Other data still missing:
Heights/Lengths/Wingspans of certain G-Max Pokémon, i.e. Toxtricity, Toxtricity-Low-Key, Snorlax, Sandaconda, Orbeetle, Machamp, Lapras, Kingler, Hatterene, Grimmsnarl, Gengar, Garbodor, Duraludon, Coalossal, Centiskorch, Copperajah, Flapple, Appletun