Mordecai (Marduk)

Problem child who's gotten the worst luck, main antagonist, very photogenic

Darkrai's chaotic creation as the first Nightmare ended up with him being inadvertently banished to the dream realm. there they ran into the newly created cresselia, and together they figured out how to use their powers and the dream realm flourished under their combined efforts. As a gift, Cresselia created their collar, a bright bit of red to their otherwise monochromic form. He created a similar gift for her. After finding out the real world was infact, a real place you actually could go to, the two talked it over and decided they should see it for themselves. finding a good point, the two stepped out.
and this is where everything kinda went horribly wrong. 

Turns out, being banished from the mortal realms shortly after his creation gave darkrai a complete intolerance to light. so stepping out into the mortal realm in the middle of the day destroyed both him and the gift he had given Cresselia. After realizing what was going on they both retreated back into the dream realm, but Darkrai was crushed by the whole event, becoming moody and bitter, pulling themselves away from cresselia and spending a lot of time alone desperately trying to figure out why it had only hurt him. All this led to an intresting encounter with a mortal's dream where he accidentally snapped the dreamer into a lucid state.
This dreamer, a murkrow by the name of Sam, encountered darkrai several more times and it was here darkrai learned that the mortal realm isn't just death light, and that there was a whole other part of it that was mostly dark, and the two theorized that if darkrai stepped out at this time, he maybe wouldn't get destroyed this time. Darkrai was understandably wary of trying again but Sam was persistent and promised to be there waiting for him. bolstered by this, they plotted out a specific time and place to try again.

The second foray out was at night and thus darkrai did phenomenally better at tolerating the mortal realm this time around. Sam indeed was waiting for him like the crow had said he would be which delighted darkrai and when Sam offered to show him what the world was like, he eagerly accepted. Sam took him home and Darkrai ended up being pseudo adopted into the Muder mob of Sam's family. He spent a long time out there learning the ins and outs of the world and his own body's limitations. Noting how dark types were generally treated including the murder he was a part of, he pitched an idea to the mob. what if, they created their /own/ place, just for dark types, so that they could be safe! in a nice dark place. the whole mob was on board and together over the next few years they founded Clandestine, the City of Shadows and Darkness. carved into a deep valley, it quickly grew and prospered. Sam evolved into a honchkrow at this time and took over the murder with Darkrai who was given the name Marduk.

It was around this time that Cresselia finally tracked her counterpart down, and ventured out of the dream realm, into Clandestine. The resulting encounter was a bit of a disaster, Cresselia was determined to drag darkrai back to the dream realm and Marduk didn't want to leave the life he had built up behind. They fought, Cresselia eventually ended up pitching a fit and fled the mortal realm again. Marduk felt bad about it, and Sam, after finding out that Marduk had been effectively avoiding Cresselia for awhile now forced him to go apologize and bring her back so he could meet her properly. This he did, and Cresselia became another fixture of Clandestine gaining the name Louise.

Life was good for awhile the city was good and prosperous. Marduk and Sam spent their time between running the city and getting Louise caught up on the workings of the mortal realm. The three grew pretty close, but Lulu always felt uncomfortable in this realm. Marduk wondered if there was something he could do about that and took to studying the planer realms and how maybe he could bring the dream realm a bit closer, at least in Clandestine to make her feel more at home. He spent a long time carefully concocting a plan to do just that, but when he finally put it into action the resulting snap or the realms completely annihilated Clandestine and everyone in it. Marduk was left with the Dark Crater a large pit that ironically enough had succeeded in breaking the barrier to the dream realm and allowed free manipulation of the area. unable to face Lulu after the horrible thing he had done to their home, he gave up his name entirely and fled.

Darkrai spent a long time avoiding everyone after that, traveling the mortal realm in the shadows, occasionally returning to the dark crater to attempt to clean up bits of it, but ultimately only making some progress. Eventually he runs into the Yevetal, Yona, who was also running from his own issues, and the two bonded. Eventually they both decided that there was indeed a gap felt in the world, an imbalance that needed filling, and they set out to try and fix this. Meanwhile, Lulu in her own quest to try and hunt darkrai down again, found Yona's counterpart the Xerneas, Xylia and teamed up with her.

the clash of ideals and the boys unwillingness to cooperate led to a lot of conflicts of which while Darkrai assisted Yona how he could, he refused to actually cause any harm on Lulu, which lead to a rather downhill series of events. and the boys eventually wound up seeking refuge in the great Black City. Upon talking with the city's leader, the Zekrom, Paragon found that their viewpoint on things made a lot of sense to him and decided to help them out how he could. this inadvertently drew his counterpart, the Reshiram Candore over to the girl's side and the whole thing escalated fairly quickly into what would be later known as the War of life and death. Darkrai did his best to both try and continue to avoid Lulu and keep things on task but everything kind of spiraled out of control when Swords of Justice were made as a direct result of the war and the Kyurem showed up. The whole mess was brought to a head when the Victini joined the other side of the war and when faced with them very clearly gaining victory, Yona responded by tearing the Victini apart. This resulted in the great elder goddess giratina coming out and pulling up a thing from the core to effectively seal off everyone involved in the war. Darkrai was sealed at the spot where he had first stepped out of the dream realm, the New Moon Island and he remained that way for many years.

About fifty years later he was released by a subordinate of his, a sableye by the name of Nova. Instructing Nova to go release Yona next, and without Lulu to chase him down for the time being he stayed between the dream realm and Clandestine to try and salvage it how he could. after a long time of spending far too much time alone doing this, and growing more frustrated with the fact that all of his previous efforts to help others proved to be disastrous failures at every turn, he decided he would instead turn his efforts inwards and try and do something for himself and try and fix the light. after a lot of experimenting with himself and the environment, he discovered that upon removing one of the time gears from it's place in the northern continent stopped time, and thus the light, from effecting the area, he set out on a task to collect them all and freeze time on the northern continent.

this unfortunately had the side effect of pushing the already worn thin dialga into a primal like state and the Celebi, Lonnie proceeded to step in and with some help put a wrench in and eventually dismantled Darkrai's plans by going after him in the dream realm itself, using the by now released Lulu's powers to do so.

Darkrai finally gave all hope up, relinquished the rest of the time gears in a series of puzzles, and retreated back to The Dark Crater. This is where Lulu, along with another incarnation of Sam eventually found and finally reconciled with him. They then worked at rebuilding Clandestine out of the Dark Crater together.