The audience see's a part of the Multiverse, A.K.A the place where many worlds are kept: many bubbles of varying colors, transparent enough to let stars, galaxies and planets inside them visible.
"There was an idea.", NiGHTS narrates.
NiGHTS, in a world with a dark gray sky and solid black surface, is holding next to her mouth the Persona (mask) of her brother, Reala.
"To bring together, a group of multi-universal heroes.", Dipper Pines narrates. Pacifica is struggling to get up from the crater inside a castle. Dipper and Mabel look down to their friend and look at each other, surprised.
"To see if we could become...something more.", Steven Universe narrates. Steven opens the window of his home at nighttime, as Peridot approaches him, showing she has a orange stone stuck on her right cheek. Steven swiftly holds in a comforting way his gem friend's hand.
"So when they needed us...", Knuckles narrates. "We could fight the battles.", Kris, Susie and Ralsei complete. Knuckles is standing alongside the Delta Warriors agains't the sunrise. Knuckles looks at the three prophetic heroes, who look back at the protector of the Master Emerald.
"That they never could.", Pearl narrates. Bismuth presents a shy-looking Pacifica to Pearl, who simply smiles to the Northwest girl.
The screen changes to black before heroes from all the works present in the crossover appear, agains't a colorful background and some of their quotes. The logos from the works that developed them appear right afterwards.
…
In the Castle of King Dedede, in Dreamland, Dedede himself, along with Garnet, Amy Rose, Star Butterfly, and NiGHTS, looks to their backs as they hear panic outside. Meta Knight, who's standing over a closed chest, notices the commotion earlier, so does Dipper and Mabel Pines. Pacifica, meanwhile, is holding her forehead in pain.
"In time...you'll know what it's like to lose.", Zalgo narrates.
NiGHTS floats to the door, giving a small look back at her teammates, before opening it, revealing Waddle Dee's, Waddle Doo's and other inhabitants of Dreamland running around in panic.
Steven, Cream and Cheese are resting on one of Halberd's inside halls.
"To feel, so desperately that you're right...yet to fail. Alll the same.", he continues.
Cream points out to Steven that his pink gem is glowing. Steven, Cream and Cheese look out in one of the Halberd's windows, only to get a shocked look in their faces. In the skies of Dreamland, there's a tear oozing black goo out of it, and it's enough to make the children and the chao gasp in horror. Tails runs to the Halberd's deck to warn about it to Meta Knight, Dedede, Bandanna Dee, Kirby and the rest of the Crystal Gems.
"Dread it..." Garnet, Amy Rose, NiGHTS, Star Butterfly, Dedede and Meta Knight stand in the middle of the destroyed streets of Dreamland. NiGHTS is holding Reala's mask between her hands, and Garnet takes her visor out of shock, revealing her three eyes.
"Run, from it..." Three pairs of feet are shown walking/flying through the Dream Gate of Nightopia, while a giant, blue cape floats among them. Reala seems to be handing to them his own Persona mask, whose circle-shaped gem begins to glow.
"Destiny still arrives." A red-and-black blast of electricity transforms into a portal, which Zalgo steps out of. He has a deadly glare set around the place as the portal fades away.
"Evacuate our worlds.", Rayman says. Steven, Cream and Cheese arrive to a mountain nearby enough of the tear. Steven has his shiled summoned in one hand, and Creams is wearing a different, longer outfit. She also has a orange umbrella with a hook on one of her hands.
"Engage all defenses!", He continues. Kris is lifted high into the air, screaming, as his red SOUL is lifted upwards to fit within a thigh space, with a beam of raw, red energy surrounding it.
Pearl summons one of her spears as she fights the Beldam and Uramiko the Cat Grill, only to throw it at her back. A being disguised by the shadows moves his body and gets the spear.
"And get this guy some speed shoes.", Rayman finishes. The figure steps out to reveal he's actually Sonic the Hedgehog, sporting a serious look in his eyes but his typical, confident smile in his lips. Amy Rose, holding her Piko Piko Hammer and looking at her back, can't help but gasp in relief.
The next scene shows the Leg Ships from Pink Diamond landing into the shining grass of Green Hill. Star Butterfly is fighting agains't someone, branding her pink diamond-emblazoned sword.
Garnet de-summons her own gauntlets, as one of the Halberd's bat wings falls into the the same shining grass from before. Susie easily knocks down a shadow-like demon monster with her ax, as Rayman knocks down another one with his fists.
Steven, Cream and Cheese, caught by Zalgo's fingers, are slammed down agains't the ground, as they visibly struggle agains't the grip of the Hivemind of Chaos.
"Fun isn't something one considers when balancing the multiverse..." NiGHTS turns her neckless head backwards, as Peridot, wrapped over dark plants, is stabbed on the right cheek by a knife held by a pale hand in a dark green sleeve. The green gem is explictly screaming in pain, but in a sort-of comical way.
"But this..."
Zalgo places the blue Space Stone onto his own Infinity Gauntlet. He carefully looks at the weapon, now with only four stones remaining for him to reach complete godhood.
"Huhuhuhuhu..."
NiGHTS holds a fist close to her pinkish-red gem, fiercely determined as a demonic shadow covers her. He Who Waits Behind the Wall walks forward slowly, closing his gauntlet-covered fist with metallic sounds as the two stones glow.
"...does bring a smile to my mouths."
Zalgo effortlessy punchs down the renegade Nightmaren NiGHTS, who falls on the ground with a soft noise.
Bismuth shapeshifts one of her arms into a sword, standing along the rest of the heroes, and a army formed mainly with Dreamland's inhabitants and gnomes from Gravity Falls. Rayman looks through everyone before summoning the claws of his red, metallic gloves. Lapis flies over the war, blasting the enemies with water balls of energy as she yells.
The heroic army and Zalgo's army run through the extensive battlefield, aiming at each other.
The last shot shows that, from left to right, Bismuth, Star Butterfly, Sonic the Hedgehog, King Dedede, Pearl and Rayman, alongside many other allies and a whole army behind them, are running forward in a formation, ready to battle a war they never thought they would make part of and save the day.
MULTIVERSE: INFINITY WAR
Meta Knight is panting heavily, tired, with his armory (including mask) broken, and his cape dirty. He looks to his front, his eyes glowing in shimmering green.
"Who the hell are you girls?", Meta Knight said with the breath he managed to get.
From left to right, Kebako, Ami & Yumi, Ib, Coraline, Frisk and Chara Dreemurr, Cornet Espoir and Kururu, Liddell and Pucca are shown looking at the knight of Dreamland and leader of the Meta-Knights. While nearly everyone is more than confused, Pucca sports one of her smiles before waving at Meta Knight.
[Coming "I Don't Know When"...]