The Omega Portal is a portal located on a lone island in the tumultuous waters of Andros that leads into the Omega Dimension.
Overview
Pre-Series
Originally, the most dangerous villains that existed within the Magic Dimension were sent to a secluded island on Andros once they were captured, but room on the island quickly became scarce with every new prisoner. To combat this, three wizards, one of which being Taboc the Wise, were called to create the portal into Omega. It was later reinforced with magic to ensure that none could open the Portal from the other side.
Series
Season 3
The Omega Portal is first seen in the episode "The Princess' Ball" from the perspective of the Omega Dimension when the Trix lure the Ice Serpent and use an ice blast of its to blow the Portal open. The witch trio, led by Valtor, who was freed moments before, emerge from the Portal on Andros and begin to seize the realm as part of Valtor's conquest.
From here, Valtor imprints any and all mermaids he comes across with his mark, forcibly transforming them into horrid mutated versions of their former selves that attack everything around them. He and the Trix go on to use the island of the Omega Portal as their base of operations to keep Andros under their thumb as they ravage multiple other realms for either their strongest spells and artifacts, or to simply cause turmoil for the Winx by forcing tragedy into their personal lives.
By "Alfea Under Siege," the villainous quartet have grown tired of the island as they no longer have room to store anymore spells and artifacts, and there is not much havoc they can wreak with Andros under their total control. To fix this, they take over and move into Cloud Tower.
The ramifications of Valtor having forced the Portal open begin to become more apparent in "One Last Fluttering of Wings," where the Portal, now completely unstable, starts collapsing. This causes powerful tremors to rock the waters of Andros as beings who were locked within the Omega Dimension make their escape through the crumbling Portal, and go on to wreak even more havoc on the realm.
Everyone on other realms also become aware of this disaster as Andros and many other realms will face total destruction should the Portal completely collapse.
Valtor and the Trix observe the disaster unfolding on Andros from the safety of Cloud Tower while the Winx, determined to save Aisha's homeworld, travel to Andros to figure out a way to close the Portal up.
The group ends up getting split in half as they do their best to free the mermaids from Valtor's influence and round up as many rogue criminals as they can. With help from Taboc the Wise, one of the three wizards responsible for the creation of the Portal, Aisha, Bloom and Tecna are led to it, only to see that the Portal has opened up more and collapsed further. Taboc attempts to safely destroy the Portal with an incantation, but the scroll the incantation is written on quickly gets sucked up into it, leaving the group with no other option but to close the Portal from the inside if they wish to save Andros. Bloom and Aisha attempt to enter the Portal but are blown aside, so Tecna decides to try and close the Portal.
She ends up being the only one who could safely step into the chaotic funnel of magic and, upon earning her Enchantix from the act of risking her life to do so, uses her newly acquired Fairy Dust to seal the Portal shut. Unfortunately, just before it completely closes, Tecna is sucked into the Portal and trapped within Omega as it shuts behind her. Frantic, the Winx begin to cry for their lost friend as Musa desperately pounds on the Portal's surface as if it would bring Tecna back.
Sometime after his humiliating defeat at Lake Roccaluce in "Wizard's Anger," Valtor ambushes the Specialists and kidnaps them all, taking them to the Omega Portal in a last-ditch effort to eradicate Bloom and the Winx once and for all. He leaves Helia to relay his message to the Winx and lead the girls right into his trap during the season finale.
When the Winx, aided by Helia and Nabu, arrive on the island of the Omega Portal, they are immediately met by the sight of an unconscious Timmy trapped within a raging cyclone of wind, showcasing how Valtor had salvaged his Spell of the Elements and has repurposed it to serve as personalized traps for over half of the Winx. And so, as the group ventures further into the island's interior, the Winx are split apart to face said personalized traps as Tecna stays behind to free Timmy and faces an elemental monster in his form made of wind, Stella saves Brandon from a flood only to face an elemental monster of water in his form, Musa frees Riven of his petrification only to face elemental monster made of rock in his form, and Bloom braves past a wall of fire and ends up facing an elemental monster made of fire in the form of Sky. The Winx remain powerless to defeating their respective elemental monsters until Bloom launches a her Dragon Fury, which tracks Valtor by his spark of the Dragon's Flame and knocks him unconscious, breaking his concentration over his Spell of the Elements.
As the Winx, Helia and Nabu travel to the center of the island to confront Valtor, the evil wizard in question wakes up to find himself in Limbo, where he is greeted by the images of his mothers, the Ancestral Witches, who berate and degrade him for his constant failures despite all the power he is supposed to wield as he let his vengeance against the Domino Royal Family get the better of him. They then strip him of his human form and most of his sanity, leaving the Winx to face his bestial demon form when he wakes up.
Valtor's demon form proves to be too powerful for any of the Winx even as they fight together, which leads to Bloom to concentrate her being into the essence of the Dragon's Flame within her and have it meet with Valtor's dark essence within his raging body. Using her Dragon Fury one more time, Bloom unintentionally reverts Valtor back to his human state within Limbo.
Bloom and Valtor's confrontation within Limbo leads to the latter's demise as Bloom, adamant in her refusal to listen to any more of the evil wizard's lies, finally extinguishes his spark of the Dragon's Flame with her Fairy Dust, causing his demon body to explode. With Valtor gone, Bloom's essence returns to her unconscious body and she is met with a loving embrace from Sky, who was under the impression that she had died during the fight. And so, with the Specialists rescued and another threat to the Magic Dimension defeated, the Winx and Specialists leave the Island of the Omega Portal and return to Magix for a celebratory end-of-the-year party at Alfea.