Connla  is powerful ghost who wanted to unleash his army on Earth by permanently opening the veil to the other side.
Connla was the son of the mythic hero Cuchullain.  A piece of truth grew into a legend about him. The essence of his ghost or another unrelated entity absorbed and imprinted the retellings into an identity.  The ghost of Connla first manifested during the festival of Samhain. He attempted to widen the already-open doorway to the other side. Ultimately, he was believed to have been banished by a druid that discovered his true name. He was not seen for centuries. 
During active construction of New York's City Water Tunnel No. 3, one of the miners, Murdock the Miner noticed an opening in a wall illuminated with an orange glow. He ventured inside the side cavern and found a man made chamber. He radioed his chief to report he found something weird. The chief reminded him he wasn't paid to find weird stuff and wanted to call in the discovery but Murdock noticed a small chest on a pedestal and reckoned it was worth something. Rather than turn it over, he wanted it for himself and picked it up. Connla was released. The Ghostbusters were called into investigate. Murdock survived the ordeal and talked about opening a box found in a side cavern. Egon Spengler noticed strong readings and didn't think it was the typical ghost of an accidental victim. They went into the cavern where Egon picked up an extraordinarily high P.K.E. signature from the chest. He wanted to run tests and learn more about where it came from. Peter Venkman directed everyone up above where Connla was hovering in a seated position. Ray Stantz elected to communicate rather than blast at it and risk a fatal cave-in. He identified himself then asked Connla if he was lucid, how long he was underground, and how he first came to arrive in the tunnel. Connla warned Ray there was great power in a name and he shouldn't give his away so freely or it could be used to destroy him. Winston Zeddemore took that as a threat and drew his Proton Pistol. Connla denied that was threat, yet, then vanished. Suddenly, a swarm of Bat Spectral Constructs poured out the side cavern. The Ghostbusters ran to the elevator and took it back up but the ghosts caught up and slimed them on their way to the surface. The crew asked if it was safe to resume work. Egon verified P.K.E. readings dropped but he suggested they wait at least one day and promised to have a P.K.E. alarm installed in the meantime for their safety. Peter inquired if anyone had a guess who they encountered. Egon believed the Irish accent, unique appearance, and the chest was enough clues to get started with.
Jenny Moran started up on research while Ray took a shower to remove the ectoplasm. She found an entry in "A Book of Pagan Rituals" were a drawing matched their description though she thought his head looked more like a turnip than a pumpkin. Ray looked at the vague entry in "The Old Book of Magic" and learned the entity's connection to Samhain, his goal, and defeat. Ray recalled druids didn't have a tradition of writing so the real name was lost to time. He hoped the Ghostbusters' modern arsenal would be an adequate substitute. Jenny advised him to be careful. They were interrupted by the untimely arrival of Ron Alexander for proton equipment recertification. The Firehouse got a call from Grand Central Station. Since Peter nor Winston were answering their phones, Kylie Griffin and Ron went with Egon and Ray to investigate. Kylie cleared the station with Paranormal Contracts Oversight Commission evacuation protocol "Code Dan." Ron bragged Chicagoans wouldn't comply with that and probably couldn't spell "evacuate." Kylie bet they loved Ron out in Chicago. She suddenly got a ping on her P.K.E. Meter. She quickly turned and fired but Connla contorted his body and dodged the proton stream. He mistook it for magic and asked them if they were druids. Ray denied it and nicknamed him "Sammy" after the festival of Samhain but Ron pointed out that was weeks away. Connla agreed but admitted the veil was so thin, he couldn't resist acting early then punched Ron. Egon got out and hid a Proton Grenade behind his back. Ray and Egon joked at Ron's expense. Ray didn't think he could be that bad since he punched Ron. Egon threw the grenade at Connla's back and blew his head off. Ron was slimed in the process. Ray clarified he was just joking and punching Ron wasn't a metric for goodness. Egon contended it was one for basic sentience. Kylie wrangled Connla's body with a stream and Ron trapped him. To their surprise, Connla broke out of the Trap. He was insulted he was attacked from behind and entrapped before they even knew his real name.  He grabbed Kylie by the throat, reformed his head, enlarged his size, then became inflamed. She noticed a ring on his right middle finger. Ron fired an atomizing stream and dispersed him. Kylie fell to the ground and read him the riot act. She pointed out the thing they couldn't trap would reconstitute in a few days having absorbed the city's ambient psychokinetic energy.  Egon regretfully agreed dispersal was the right play because it bought them time to come up with a permanent solution. Ray asked who was going to call Walter Peck and inform him of the mess. The station was covered in Yellow Slime. Kylie quickly replied "not it."
As a result of being in direct contact during the dispersal, a latent mental link was forged.  In the few days before Connla's reconstitution, Kylie had a precognitive dream while she slept in the Ray's Occult Books office. In the dream, she and the four original Ghostbusters came upon high readings that kept climbing and shorted out a P.K.E. Meter left over from the Real Ghostbusters of Dimension 68-R. Connla's Army surrounded them and began to swarm. As they discussed fictional detectives, Connla appeared. He agreed it was going to be a long night and knocked the Ghostbusters off their feet. He declared the veil to the other side would open permanently, more armies would come, and night would last forever.  He dropped Kylie into his head. She awoke and went to the Firehouse to share details of the dream with the others. Egon noticed strange readings picked up by the Dream Analyzer Helmet but lied to her they were normal to assuage her fears. Kylie admitted she felt physical sensations during the dream. Egon asserted no matter what, they took dreams seriously. Peter contended he never took his seriously. Janine added they all learned that lesson already. Peter brought up the ghost had an Irish accent and hinted at a connection to Kylie like with Janine Melnitz and the Draugar. Egon doubted it. Kylie revealed her great-grandfather chose her family's surname when he immigrated to America because it had a good ring to it. She realized something mid-sentence and ran off to double check her theory. With knowledge of the army coming, Egon went to work preparing for the possibility. He dug out a Remote Portal Access Band from a box.
After a few subway stops, Kylie returned to Ray's Occult and confirmed her theory the ghost was Connla. He had a real sticking point with his name, was quick to fight, and wore a ring. She called up Ray's cell phone and informed him of the good news. Ray had calculated Connla would return no earlier than next Wednesday at midnight. Evidently, he didn't have all the factors at the time. On Friday, after 3 pm, the Ghostbusters, Ron, and Kylie flew to Liberty Island in Murdock's helicopter. Kylie shared her findings and admitted the legend she keyed onto was based on a piece of truth or the essence of the ghost itself absorbed and imprinted the retellings into an identity. She joked he was Rumplestiltskin then went on to reveal she thought he was the son of Cuchullain. She asked Egon's friend to leave as soon as possible. He pointed out they would be stranded. She contended the helicopter was loud and she wanted to make sure Connla heard her. Ron fired into the mist but tons of ghosts emerged from it. Kylie recognized the ghosts from her dream. Ron wanted her to hurry up because he didn't want to die on a landmark. Kylie readied a Trap and called out to him. Connla couldn't believe she knew his real name because it was never written and recorded. He extended his fingers into the ground. They emerged and grabbed everyone. Kylie hit the pedal and began to reel Connla into the Trap. He called out to his army to help him. To their surprise, the ghosts tried to pull Connla out. Peter and Winston threw out two more Traps. Connla ordered the ghosts to destroy the Ghostbusters then free him. Kylie realized more and more ghosts were being summoned and they didn't have enough Traps. She regretted sending the helicopter away. Egon assured her it was fine. He used his access band and teleported away then returned with the rest of the Chicago Ghostbusters, the Real Ghostbusters of Dimension 68-R, the Extreme Ghostbusters of Dimension 68-E, the Ghostbusters of Dimension 50-S, the Ghostbusters of Dimension 80-C, and Mike the Golem joined the battle. In no time, they finished trapping every ghost.
Connla is based on the son of the mythic Celtic hero, Cuchullain. He became a fearless warrior that was immune to most magic and could not be contained. Connla was his son from a Scottish warrior named Aoife and was raised by her. When Connla was seven years old, Aoife gave him a gold ring left by Cuchullain. Cuchullain wanted Connla to find him in Ireland when he became of age. Aoife laid down three conditions: he couldn't turn back once he started his journey, he must not turn down a challenge, and he must never tell anyone his name.  Connla's weakness in the 2018 Annual was also tied to mythology and was a common theme. Knowing the name of a magical creature meant having control over it.
Connla can levitate, disappear and reappear, reform body parts, manipulate his size, and extend his fingers. He had the unique ability to break out a Trap until he was correctly identified by Kylie and command a legion of ghosts that remained loyal to him and carried out his orders even after he was trapped.
- Connla's look was inspired by the old turnips the Celts would carve on All Saints Day to ward off evil spirits. 
- On page 2 of Ghostbusters Annual 2018, in panel 3, carved atop the pedestal is the Wheel of the Year. One circle represents life and the other represents death. Joined, they become infinity.
- On page 4 of Annual 2018, Ray attempts to communicate with Connla much like he did with Gozer in the first movie.
- On page 8 of Annual 2018, Peter refers to Connla as "Great Pumpkin," a nod to the Charlie Brown Halloween special "It's the Great Pumpkin, Charlie Brown".
- IDW Comics
- ↑ Kylie Griffin (2018). IDW Comics- "Ghostbusters Annual 2018" (2018) (Comic p.21. Kylie Griffin says: "-- CONNLA!"
- ↑ Kylie Griffin (2018). IDW Comics- "Ghostbusters Annual 2018" (2018) (Comic p.29. Kylie Griffin says: "I think this thing believes it's the son of the mythic hero Cuchullain."
- ↑ Kylie Griffin (2018). IDW Comics- "Ghostbusters Annual 2018" (2018) (Comic p.29. Kylie Griffin says: "All that dovetailed so well the elements of an Irish legend, I figured it could be related. Maybe the legend was based on a piece of truth, or the essence of the ghost itself absorbed and imprinted the retellings into an identity."
- ↑ Ray Stantz (2018). IDW Comics- "Ghostbusters Annual 2018" (2018) (Comic p.9. Ray Stantz says: "Says this fella "...first manifested during the festival of Samhain, trying to widen the already-open doorway to the other side." Is it me or do a lot of entities have that particular goal lately? Hmm... "Hasn't been seen in centuries, believed to have been banished by a druid that discovered his true name..." But, of course, since druids didn't have a tradition of writing things down, the name was lost."
- ↑ Connla (2018). IDW Comics- "Ghostbusters Annual 2018" (2018) (Comic p.18. Connla says: "You don't even know my name...and you dare think you can trap me?"
- ↑ Kylie Griffin (2018). IDW Comics- "Ghostbusters Annual 2018" (2018) (Comic p.20. Kylie Griffin says: "That thing we couldn't trap is gonna re-constitute in a few days, having absorbed a ton of ambient psychokinetic energy in the process! You just gave it a power-up, you idiot!"
- ↑ Egon Spengler (2018). IDW Comics- "Ghostbusters Annual 2018" (2018) (Comic p.24. Egon Spengler says: "You were in direct physical contact with the entity when it was dispersed. So there's some possibility of a latent mental link."
- ↑ Connla (2018). IDW Comics- "Ghostbusters Annual 2018" (2018) (Comic p.23. Connla says: "The veil will open permanently this time. The armies will come, and finally, night will last forever."
- ↑ Harpur, James (2008). Celtic Myth: A Treasury of Legends, Art, and History, p. 36. Routledge, New York NY USA, ISBN 0765681021. Line reads: "Cuchulainn not only spared Aoife's life but he also fell in love with her. Soon she came pregnant with his son. Cuchulainn, however, had to return to Ireland. He told Aoife that their son should be called Connla. He gave her a gold ring to put on Connla's thumb when he was old enough to fit in. At such a time, Cuchulainn instructed, Connla was to set out for Ireland to find him. The boy was to tell his name to no one, step aside for no one, and never refuse to fight a challenger."
- ↑ Dapperpomade Tweet 3/15/18
- ↑ Narrator (2018). IDW Comics- "Ghostbusters Crossing Over Issue #2" (2018) (Comic what came before page). Narrator says: "So not long ago, the Ghostbusters were fighting an entity with a legion of followers - to help mop up the followers, they called in help from several other dimensions."