No joke, here are some very good X-Files fics involving April Fools' Day. Enjoy!
April Fool's Day Series by GirlGone
OK, someone challenged me to write a story that wasn't an X-File, a serial killer study, a girlfriend story or a mushy Scully-Mulder romance. I thought about it for awhile and this is what I came up with.
April Fools? by A. Dean
Written in response to Deb's picture challenge from the US magazine.
April Revolution by Foxie Meg
"The streets of Paris are burning once more."
bad ideas in bed by @wtfmulder
Drabble; R; fluff, smut; Scully x Reyes; Prompt: “It’s called a prank.”
Bloody Hell by @baronessblixen
Happy April Fools’ Day! Mulder is just trying to pull a little prank on Scully... it doesn't go well.
Fifth Day in Paradise part 1, part 2 by Kate Rickman
En route to the scene of an X-File, Mulder and Scully are stranded in the snowy wilderness after their rental car breaks down on a deserted road. Instead of finding their way back to civilization, they stumble into a treacherous plot that could cost them their lives. Through it all, Scully struggles to accept her deepening relationship with Mulder.
Folly by @rivkat
Starts in early Season Four; after TFWID, Season Four doesn't happen; instead we take a strange journey into conspiracy, experimentation, and speculation.
Leave A Message by Amanda Finch and Tim Scott
Our favorite agents' terrible, horrible, no-good, very bad day or "When Good Pranks Go Bad". (Check your local FOX listings.)
The Man Without A Trace by @syntax6
Insanity
Outrunning Moirae by Jennifer Oksana and FirePhile
Mulder gets his usual vague information from an informant. It leads him across the country into unbelievable government mischief. Meanwhile, as Scully tracks the case from DC, she starts to question everything, including her own identity. Set around season 5.
Wrapped in the Wind Series by RocketMan
This is a Romance with Mulder and Scully and a little baby girl. Much like The Emilys, if you liked those.