Finally caught my Mimikyu and completed my team! I now have:
Decidueye: Brave Nature. Maybe I should have reset until I got an Adamant one, but I'd been at it for two hours already, and it's not like there aren't uses for a slow U-Turn. Anyway, I'll probably switch to one with its Hidden Ability for competitive purposes, once that becomes available.
Snorlax: Adamant Nature. Using it because the event made it so easy to get a good one, but it's just as badass as it was when I caught and used my first Snorlax. (Seven years ago, in my first Pokemon game, SoulSilver!)
Oricorio: Timid Nature. I was just planning to use her until I filled out the rest of my team, but then I caught a Timid one by sheer chance, and this team is really low on Special Attack. Also, she's so adorable. Hoping to find Red Nectar soon.
Midday Lycanroc: Jolly Nature. I found her a bit under-powered when she first evolved, but now that she has Rock Slide and Crunch she's doing great. (Accelerock will be useful competitively, but Rock Slide is so much better for Zubats and Trumbeaks that like to call all their friends.)
Toxapex: Quiet Nature. Completely worth the time it took to catch a female one with Merciless and breed her for a decent nature. Baneful Bunker followed by Venoshock is a mean trick to play on the AI, but so much fun <3. Looking forward to trying her out in Trick Room.
Mimikyu: Careful Nature. It took me an hour to find one, but the first one I saw was the nature I was hoping for! (I plan to run a defensive-ish set with Bulk Up and Will-O-Wisp.) I've been in love with it since I read its flavour text on the web site, and I am not disappointed. I think the Ghost Trial in general is one of my favourite Pokemon moments ever.
Bonus boxed Pokemon: Crabrawler. Great early on, but was starting to lag behind by the time I replaced it with Mimikyu since it evolves so late. And Crabominable has too many weaknesses to fit on this team, anyway. Planning to come back to it post-game, when I'm building that Trick Room team.