I’d match you with Undertale Sans!

Sans is outgoing, though it’s your expression through your clothes and hair that draws him to you.  The way humans can change their hair so easily has always been something that fascinated him, so it immediately caught his eye(socket).  Sans also knows what it’s like to need some coffee; he tends to nap throughout the day, but when he worked in the Lab, he had a constant need for the monster’s version of coffee-- covfefe.  

When it comes to your love for soccer, he’s got an endless supply of puns about it.

“was your goal to win my heart?”

“what can i say?  i’m a real soccer for you.”

“heh, you know you get a kick out of these puns.”

For Gyftmas, Sans gets you a coffee mug that says i love you a latte.  The two of you end up going to a holiday painting class to make something festive for the wall (though Sans just paints a snowman because it’s easy and completely ignores the holiday scene you’re supposed to paint), and then go back to his house to watch holiday movies on the couch where he ultimately ends up napping halfway on top of you.

Crossover fic like AU crossover?  If it’s something like SSLL with a ton of AU skeles in one place, the most important thing is to clearly establish which skele has which nickname (try to work that in as soon as possible, because there’s so many times when people use AU’s other than US/UF with the UT bros, and it takes me a second to figure out who they’re talking about by the descriptions.) and who’s talking when.  If you have several skeles that use lower-case or upper-case in the same conversation, it gets super confusing to tell who’s speaking when if you’re not clear about it–especially when they have similar personalities.  

I always try to make sure it’s obvious, even if it’s just something like:

“paps has been watchin’ mtt since mettaton’s big de-boo,” Sans claimed.

Stretch chuckled.  “same with blue and napstaton.  gettin’ their own show really seemed to lift their spirits.”

Blackberry appeared aghast at the implication.  “WAIT, WHAT ARE YOU IMBECILES TRYING TO SAY?  THERE’S NO WAY NAPSTATON’S A GHOST!  HE’S A ROBOT!  ARE YOU BLIND??”  He turned to Mutt.  “RIGHT PAPY?”

“right as always, m’lord.”

Edge crossed his arms.  “AS MUCH AS I HATE TO SIDE WITH HIM, THERE’S NO WAY METTATON’S A GHOST!  HE’S A SEXY ROBOT, OBVIOUSLY–NOT A LAME GHOST!!”

With that, you can tell who’s speaking when.  I feel like that’s really important in AU crossovers.  

If it’s a crossover fic with one timeline crossing into another, my advice is to showcase the differences in the characters’ personalities–but also the underlying similarities.  For example, some of my favorite Underswap/Underfell crossover fics involve showing that despite the fact that Stretch has Sans’s personality, he still has quite a few Papyrus traits deep down.