Sorry you've been feeling like poop. I've got two head-canons involving everyone favorite glow-y bird man, one funny, one kinda sad.
Funny one - Marco's ticklish across his chest and his sides. Adelaide, an self-insert/OC that I pair with him, found this out quite by accident and then proceeded to chase him all across the ship much to the amusement of his brothers.
Sad one - He's a phoenix, so he's gonna outlive everyone by a few centuries. And when the time comes, he's just gonna let his flames consume him. I've actually written a little one shot on this one, but I'm just anxious about posting anything on here or Ao3.
I love both of these ^_^
That second one, though, oof.
And hey, if you ever decide to post it, let me know, I'd love to read it <3 I know how scary that first step can feel, so don't feel pressured ^_^