Arise Chickun is a rebranded meme, fusing the old Scootaloo chicken jokes in the fandom with a catchphrase popularized by Aqua Teen Hunger Force. This one specifically became popularized on 4chan’s /b/ board amongst the ban-evading pony posters, then later spread amongst MLPchan's /oat/ board and Derpibooru.
The original meaning of the catchphrase actually dates back to August 2004, at the airing of ATHF's season 3 premiere.
Main article: ATHF S3E1, Video Ouija.
Rewinding back to 2004 came Aqua Teen Hunger Force’s third season premiere, “Video Ouija,” which was an episode where Master Shake is ground into a stew in Carl’s pool. In an attempt to resurrect Shake, Frylock hires “Billy Witch Doctor,” whom specializes in resurrecting chickens. After numerous pranks, the group comes together in a séance circle and begins the resurrection ritual, which despite Frylock’s questioning, was supposedly for more than chickens. The ritual would involve Billy smacking his chicken staff to the ground, urging the group to chant, “Arise, Chicken, Arise!” After many failed attempts, Frylock gets bored and kills Billy with his laser beam eyes.
MLP Season 1 - "Stare Master"
Moving forward to the summer of 2011 when the Brony fandom was evolving, Scootaloo commonly became associated with being called a chicken from MLP Season 1 episode, “Stare Master” after Applebloom jokingly corrects her “chicken call”. Shaping off this, Scootaloo’s name being associated with a chicken became a common sight in the fandom.
Forward again to December 2012 on 4chan’s /b/ board, months after the established Rule 15. The pony posters on /b/ would often start a thread with a screencap of Scootaloo with his eyes wide open, captioned, “I CAN SEE THROUGH TIME AND SPACE!” After numerous mod interceptions, the pony posters found it amusing to watch them issue bans, yet leave the threads alive. In response, they would bump the threads without topic, with the image of Scootaloo, now with a photoshopped laser eye, captioned, “ARISE CHICKUN,” and the joke caught on instantly.
Later on, one poster would make a vector of the half-lidded Scootaloo with the same expression on her face and use it as an exploitable to derail tasteless threads on /b/, MLPchan , and sometimes /mlp/.
Derailing threads with the macro, or otherwise posting it anywhere, including on /mlp/ will very likely result in a ban due to the meme being majorly seen as a “ban evading” thing on /b/.