For the fluff asks, maybe Quirk w Darkstache :0?
Darkiplier and Wilford are two of the most powerful egos.
Because of that, they have many quirks, though most of them are violent or unstable and are not necessarily beneficial to their relationship, except for a select few.
For example, Darkiplier is a manipulator, and he is very skilled at it, to an almost magical (it probably is demonic) degree. As a result, this is very good when Wilford gets into trouble, which, let's face it, is literally a constant occurance.
Whenever Wilford has an episode and goes into a murderous rampage, Dark is always the one that tries to get to him to soothe him, or he's the one who cleans up after him, including bailing him out from the police.
Demonically manipulating police and a whole judicial system is much harder and draining for Darkiplier, but when it comes to his Wilford, he will go to extreme lengths to keep him safe and at his side.
He's nearly gotten himself arrested multiple times when he's had trouble manipulating officers, and has ended up killing near full police stations in an effort to get his doofus husband out of jail.
"Dark?" Wilford whimpered as he pressed his face against the bars of the cell, looking around for his partner, whom he knew was there, able to sense the presence and see the greyscale seeping through the environment.
"Right here." Dark replied in a cold tone, appearing in front of the cell and grabbing it to pull it open, manipulating it to get over the fact that he didn't have the key. "Relax. We're going home. I've posted your bail already."
Wilford nodded and stepped forward, pushing himself into Dark's arms and closing his eyes. Darkiplier sighed and ran his fingers though Wilford's hair.
"How do you convince them to let me go all the time?" Wilford asked tiredly, not questioning as Dark covered his eyes and led him out of the holding cells.
Dark was quiet for a moment, leading the blinded Wilford over the dead bodies of officers that littered the halls, before he responded gently. "...I have my ways."
As for Wilford, he has many more quirks and charms to him, some that Darkiplier doesn't even know about, though he knows of more of them than most of the other egos.
The most beneficial powers to their relationship would be Wilford's abilities to read into Dark's thoughts and reply the same way, and his ability to manipulate reality. This benefits both of them, as Wilford can tease Dark relentlessly, but also comfort him in his times of need.
When Dark gets distressed in public, or during an ego meeting, Wilford knows before Darkiplier even registers it.
He whispers soothing words and affections into the back of Dark's mind and calms him, before he explodes and does damage to anyone else, or himself.
Other times, when Dark is feeling particularly touch starved, Wilford knows immediately, attuned to Dark's subconscious thoughts. When he gets him alone, he manipulates reality around them to give the illusion of there being more than one Wilford, then he snuggles Dark in a cotton candy cuddle pile.
While Wilford and Dark seem to be complete polar opposites, it's likely that neither of them could truly survive, or function properly at all without the other.
The bubblegum ego sensed it immediately.
He could hear the arguing voices of Dark's subconscious from the moment he saw him, watching the way his aura flickered and warped in flashes of blinding colour.
Wordlessly, he took Dark's hand and led him to their bedroom, his thumb rubbing circles on his husband's hand, soothing and gentle. He knew it had been a long day for Dark, and he needed a little bit of TLC.
Once they'd settled on the plush bed, Wilford pulled Dark into his arms and let the 'evil' ego snuggle as close as he needed, before the world warped and duplicates of Wilford, mostly just pink auras, snuggled Dark from every angle, wrapping around him like blankets, radiating love.
This always made Dark smile, half in amusement at being squished by multiples of Wilford, and half in sheer gratitude that Wil knew exactly what he needed.
"...thank you." Darkiplier whispered, his voice low and soft as he tilted his head to look up at Wilford, wearing a tired smile.
Wilford didn't respond, and just kissed Dark, letting the two of them melt into the bliss of their much needed comfort.