Audino-Mega: Harriet | The "Broodals" are evil white rabbids wich appear in the upcoming Super Mario Odyssey. The first of them is named "Harriet", and it wears a rocky helmet, just like my Audino-Mega in BH usually does.
Dialga: Partner in Time | Named after the Mario RPG game "Mario & Luigi: Partners in Time", because a trainer's pokemon is known as his partner and because Dialga is the Temporal Pokemon.
Ferroseed: FerroWeed | Portmanteau of Ferroseed and Weed.
Slowpoke/bro/king: 2slow4u | pun on the well-known phrase 2fast4u and its name.
Raichu | Dundahbolt | In the episode "Electric Shock Showdown" of season 1 of the Pokemon anime, Lt. Surge tell his Raichu to "Give 'em a Thunderbolt", but it sounds like "Dundahbolt" because of his accent.
Heracross | Hercules | Heracross is based on the Hercules Beetle. Nuff said.
Blaziken: Spicy KFC | Whats more to say? Its one hot bird!
Skarmory: Skarmoney | This one was born out a way I used to pronounce its name, my friend caught me on it and now i call it this. Though it should be called Skarmoney because it makes them stealth rocks rain!
Whismer: ASMR | ASMR videos are those vids on youtube where people make weird sounds and talk very quietly. It’s really creepy.
Blastoise: SuperCannonCatTurtle | Whats up with it’s ears? Since when do turtles have cat ears?
Landorus-Therian: Hi again! | Every player ever in the OU tier has used lando at some point it’s jut sooo common.
Electivire: Electric Gorilla | Electivire is just a mon with a design thats just so uhhhh? The most I make out that it looks like a gorilla space thingy.
Ferroseed/Ferrothorn | Robocrop | Pun on its grass type + Robocop. NOTE: I found this nickname on Twitter (I forget the user's handle)
Aurorus/Suicune | Aurora | Obvious references aside, Aurora is a name that implies majesty or beauty, much like Aurorus/Suicune.
Noivern | Boombat | Pun on boombox/Boomburst and bat
Pidgeot | Orville | Named after Orville, the pidgey from the anime episode "Fly Me To The Moon" that flew to outer space. Also named after Orville Wright, one of the brothers that flew the first airplane.
Mantine | Flipperbird | Thank purple shep for this one.
Cosmog/Cosmoem/Lunala | Nebby | Named after Lillie's Cosmog from the games. Plus that Cosmog is the Solgaleo/Lunala you ultimately catch, so the nickname fits.
Naganadel | Cephadrome | Seriously, just look at it.