Okay so to sum it up:

Since Stratus went insane, he's gone to the psych ward and came back a little better, but still has his issues.

He then destroyed Gradient's crystal and Gradient kinda left for probably 30 seconds.

Stratus adopted a dog named Ryn who's his not-so-little bodyguard.

H!Gradient (AKA Gray) proposed to Stratus, who got "mad" and then proposed right back. They're getting married at some point.

Strat has one really bad episode in the bathroom while Gradient is tormenting him and then Gradient goes and possesses H!Gradient.

Cue the creepy horror scene where Stratus is hiding in the kitchen with a ladle because he doesn't have the heart to hurt H!Gradient.

But Ryn sure does, because she bites that mf twice.

Gradient goes away after Stratus knocks H!Gradient out and ties him up. He's survived night one at Freddy's.

And here we are, night two. But instead of telling you flat-out what happened...

I wrote the full scene out.
(TW: minor body horror, Gradient)

"Guess who's back~" Gradient laughed, letting his voice echo around the quiet apartment. He waltzed out of the bedroom and down the hall, taking his sweet, sweet time. After all, he knew exactly where Stratus would be- the scientist clearly liked patterns.

"F*ck off!" came the shaky response from the kitchen. Seconds later, a bark in agreement. Of course that stupid dog didn't know how to quit. She was going to die; Gradient would make sure of it.

"God damn, what's with the hostility?" he fake pouted as he drew closer to the countertop, behind which he was certain that his target was hiding. "I've only just arrived!"

After a moment, Stratus appeared behind the counter, standing up and leaving Gradient no choice but to have to crane his neck upwards to make eye contact. Being a foot shorter sure did kill the ominous mood. The taller man held the same ladle from the previous night in his trembling grip as he spoke.

"This is your last warning," he said, his voice wavering. "Leave us alone before you just make it worse on yourself."

Gradient just shook his head and laughed. Stratus was pathetic for thinking he could intimidate him, and they both knew it.

"How the yza am I gonna make this worse on myself?" he taunted, crossing his arms and chuckling. "What are you gonna do, science me to death? Knock me out like you did last time?" He shook his head for a moment, smiling before adding, "Well, spoiler alert, I always come back."

To his annoyance, the dirty-blonde just gave a half-hearted smile. "Actually, I won't science you to death this time. Come on, take a step forward if you want. But that's your last warning."

Something about his words was different than the other times, but Gradient highly doubted that he was capable of actually harming the body that he was possessing. Stratus wouldn't dare hurt Axar. Gradient was practically invincible, and he was going to take advantage of that.

"Whatever you say~!" he giggled, taking a step around the corner and into the kitchen, grinning maniacally at Stratus.

The scientist just shrugged and said, "I tried to warn you. I guess... you just wanna have a bad time."

"Maybe I do." Gradient kept smiling as he advanced. Oh, was he going to enjoy this. Stratus really thought he could bluff his way out of this one, but there was no chance.

"Alright," Stratus sighed, sticking one hand in his pocket. Was he trying to pull something out? No, he wasn't. He was just keeping his hand in one pocket. So he was just trying to make it worse for himself, then. Did he want to die? "Come and get me."

Gradient lunged forward, closing his cold grip around Stratus's neck. "So I will."

The man seemed unfazed, even as he was shoved backwards in a slightly embarrassing attempt to toss him to the ground. After recovering from his stumble, he leapt forward, catching Gradient off guard. The next thing he knew, he hit the wall with a thud. But the adrenaline of being able to finally finish off this visehj prevented him from feeling any pain. He jumped at Stratus again and sank his teeth into his arm. Stratus yelped in pain before promptly throwing Gradient across the room. As he got to his feet, he had to do a double take, because Stratus was using this time to quickly draw something on the ground in chalk.

Ah, so that's what had been in his pocket. But as Gradient looked while beginning to approach again, he realized exactly what he was looking at. A pentagram. In fact, now that he looked at the countertop, there were a few unlit candles sitting on the surface, just waiting to be used. How strange.

Stratus flicked out a Swiss army knife from his other pocket, his storm blue gaze fixed on Gradient. Gradient shook his head and laughed again at the science prodigy's stupidity. "What, trying to exorcise me? Hah! I'd like to see you try!"

However, when Stratus simply smiled and narrowed his eyes defiantly, Gradient felt a small flicker of confusion inside of him.

"It's not an exorcism," the dirty blonde said before slicing his palm open with the knife.

The blood dripped onto the floor inside of the pentagram, which then began to glow an eerie red as the candles lining the countertop flickered to life in a similar scarlet hue. Gradient stared at the scene, puzzled. "Well then, what are you doing?"

"Just saying hello to an old friend." And with that, a massive creature erupted from the pentagram.

Gradient jumped back in surprise as he tried to process what he was seeing. The creature was long and draconic, seeming to be made of inky black shadows save for the four glowing red eyes, curving red horns, and wicked-looking spikes jutting out along its spine all the way to the tip of the arrowhead tail. He stood there for a long moment before composing himself once more and standing his ground again, though slightly further back.

The eldritch demon blinked for a moment before seeming to notice Stratus and commenting in a distorted yet smooth voice, "Well, this is a surprise. Aren't you the one who got rid of me? Well?" He flicked his tail in anticipation.

Stratus then shifted his attention back to Gradient and said, "Last warning, Gradient. Leave me and Gray alone for good or you won't like what happens next."

This seemed to pique the interest of the demon next to him. But Gradient wasn't about to let them intimidate him. Besides, the demon looked like it was more looks then skills. It was probably just a minor demon.

Gradient laughed once more. "You think I'm shaken by some demon? I am a demon, visehj! Bring it on!"

Stratus and the demon exchanged looks, as if trying to communicate with each other telepathically. Perhaps they were. The demon extended a hand of wickedly sharp claws, and Stratus hesitated for a brief moment before taking it and shaking.  In the blink of an eye, the demon was gone, and a swirl of black liquid entered his body through his eyes and mouth. Caught off guard by this, Stratus stumbled backwards and out of the kitchen, leaving Gradient's field of vision.

Gradient just chuckled as he walked towards where the scientist had gone, overtaken by the terrible decision he'd make. "Stratus, you fool, you should know to never make a deal with the devil."

He stepped around the corner with a grin, but something felt very wrong as he did so.  Obscured by shadow was Stratus, but he seemed even taller somehow. 

"But what if the devil..." the scientist began in a voice that wasn't entirely his.

As he took a step forward with unnatural grace, Gradient could see that his teeth and nails were considerably sharper, and both eyes were completely black save one red pupil and one storm blue.

"...is me?"

Gradient's words caught in his throat for a second.  But surely this would still be easy for him.  It was a demon and a man sharing a body, the demon couldn't have much power due to the limitations of its weak host. 

He smiled and asked, "Tough guy, eh?  Well, if you're so confident."

"You don't seem as worried as you should be," 'Stratus' commented, staring without so much as blinking once.

Gradient balled his hands into fists. "Worried, I should be?  I think not."

'Stratus' let out an unsettling laugh. "My dear friend, I don't believe you're understanding what you're up against."

Both of his irises suddenly flickered to the crimson red color as he spoke in a voice that belonged entirely to the demon, "My name is Flauros.  I am a Duke of Hell.  I can destroy you."

The candles all flickered briefly, the fire letting off black light for a brief moment as the pentagram glowed brighter, and glowing red strings suddenly shot out, wrapping around Gradient tightly and forcing him to his knees.

'Stratus's' eyes flickered back to their respective hues as he took a step closer. "What's wrong?  Not used to getting a taste of your own medicine?"

Gradient didn't respond at first, only thrashing in place, snarling as he tried to break free from the strings.  But they were too strong. 

"SON OF A-" he roared.

'Stratus' bent down in front of him, tilting his head as he said, "Now we come to the question. Do I exorcise you?  Do I strip you of your ghostly rights?  So many possibilities.  So many ways for me to snuff out your dark flame."

There was a pause before he continued. "Well?  A part of me is willing to be merciful.  I could let you go on the condition that you leave Axar and Jason alone and never return.  Would you accept this offer if it were given to you?"

The strings tightened further around Gradient, beginning to grow painful.  For once, he felt trapped.  Humiliated.  Bested.  But fortunately for him, he was able to recognize that.  He held 'Stratus's' gaze for a long moment, before quietly muttering, "Fine.  I'll leave."

'Stratus' lifted his chin and hissed, "And if you ever come back, you know that I will destroy you.  Do you understand?"

This time, Gradient refused to look him in the eyes. "Yes."

After a long moment, 'Stratus' returned to his feet, the strings snapping soon after. "Get out of here."

Gradient didn't need to be told twice.  He quickly fled from Axar's body, giving 'Stratus' one last resentful glare before leaving for what might have been the last time.

And then I drew this as a bonus for what happened after that:

(Obviously Gradient and H!Gradient belong to Addie, and if I see any of you spamming #GiveStratusSpikes I'm going to lose it. Give him spikes yourself if you really want them that badly. Yeesh.)