Ok, so this is just a slight review of how I imagine Brock and Croagunk's relationship goes.
Note: Like all the oneshots written here (unless I say so) this has nothing to do with the other stories. I imagine this is how their relationship being in the canon anime not my personal fandom. Also, this is based on "Headcanons" by Sassy_dinosaur

Who hogs the blanket?
Well, I imagine at first Brock and Croagunk wanted to keep their relationship a secret, so Croagunk slept on top of the blanket while Brock slept under it so it wasn't too suspicious. But after the secret got out, they still stuck to that because it was more comfortable for both of them. They still occasionally cuddle though.

Who texts/calls to check in the most?
Neither, Croagunk doesn't have a phone and he and Brock are around each other all most 24/7.

Who's the most creative when it comes to gifts?
Neither. When it comes to creativity, their minds turn into dead Torchics XD.

Who wakes up first?
Brock. Mostly because he has more things to do in the morning but also because Croagunk tends to sleep a lot.

Who suggests new "games"?
I imagine Brock occasionally wants to try but is still trying to figure out how they can do stuff like that.

Who cries the most during movies?
Brock, he rarely holds back crying in the anime.

Who flirts the most?
BROCK! But him being him, he's terrible at it. And I imagine Croagunk (despite never flirting before) is surprisingly good at it.

What are they like when sick?
Brock: Loopy and fever dreams that interact with whatever is happening in reality.
Croagunk: Sleeps way more than normal and unable to concentrate.

Who gets jealous the easiest?
Croagunk (just don't let him know that I imagine Brock originally noticed his feelings after being rejected so many times).

Who takes the longest to get ready?
Brock. Croagunk only has to wash his face and brush his teeth.

Who's the most organized?
Brock. When your a Pokémon breeder/doctor you need to be.

Who gets the most excited for the holidays?
Neither. Croagunk doesn't see the point in them and Brock stopped getting excited when he lost interest in pretty girls.

Who is the little spoon?
Croagunk! Mostly because he's practically tiny compared to Brock.

Who's the most competitive?
I imagine Croagunk getting a little competitive when battling but try's to keep his cool.

Who starts the most arguments?
Neither. I imagine they rarely fight.

Who suggests they buy a pet?
Croagunk is a Pokémon. Pokémon are sometimes used as pets.

What are some of the traditions they have?
Make out session at least once a day (in private of course), cuddles whenever they can, and surprise kisses (Brock is the one who normally does that because it annoys the heck out of Croagunk).

What tv shows do they watch together?
Croagunk doesn't really watch tv, but Brock occasionally makes him watch those romantic soap operas he likes. But Brock normally makes Croagunk watch them with him when Croagunk is having trouble sleeping (see what I did there?).

Who are the other couples they hang out with?
Ash and Serena, Misty and Tracey, Pikachu and Buneary, Dawn and Kenny, Chansey and Sudowoodo (that's just some of them cause the list could go on forever).

Who made the first move?
Why I'm writing this book in the first place XD.

Who brings flowers home?
Brock. But single flowers not bouquets.

Who is the best cook?
BROCK!

Who snores?
Croagunk, along with the occasional mumbling. Brock just talks in his sleep.

I mostly wrote this because I was bored and still working on ideas for the new book that I'm making soon. But for a slight preview just think about this name: Croakie