Interspace Under Siege is the 15th episode of Bakugan: Mechtanium Surge. It aired on May 29, 2011.
In the ensuing chaos in Bakugan Interspace, the Brawlers wonder what to do. Rafe makes a note that it is only the Chaos Bakugan that are on a rampage. The Brawlers then summon their Bakugan to save Bakugan Interspace. Meanwhile, Anubias says to all the other members of Team Anubias, "We can't be the champions of this place if its destroyed" so Anubias has given Bolcanon to Ben and Krakenoid to Robin. Then they leave alongside Jack but Anubias stops Noah and gives him Horridian. Noah seems happy that Anubias gave Horridian to him with Anubias seeming concerned about his "student".
Once they leave, Sellon mocks Anubias for his "concern" for Noah. He tells her to get lost. She reminds Anubias to focus with the task but Anubias mocks her for her failure against Dan and she then stops. As more and more Chaos Bakugan arrive, Marucho thinks of an idea and he decides to move all of them to Section B and delete the whole area, despite the fact that it will create huge damage in the system. Marucho then sends out an emergency evacuation but just before that Rafe gives Marucho Crosstriker for Tristar and gives Shun Hammermor for Taylean for the battle against the Chaos Bakugan. Then they, alongside Team Anubias, continue to try to move the Chaos Bakugan to Section B of Bakugan Interspace.
Meanwhile, in some type of room, somebody receives a SOS message on his computer, which was sent by Marucho and a mysterious Bakugan is seen in the background.
Back in Bakugan Interspace, the Brawlers keep bringing the Chaos Bakugan to Section B of Bakugan Interspace. They then have finally successfully led all the remaining Chaos Bakugan to Section B. Marucho then plans to fire up the erase sequence but Taylean and Shun notices that Team Anubias are still there and he tells Marucho and the others. Rafe then tells Marucho to not do it because it will delete them too and he doesn't. He then alerts them and they all run out of Area B but Noah is frozen in fear. Team Anubias just stays there with Noah.
While Noah is frozen in fear, Mag Mel and Razenoid gain more energy to be free. Mag Mel then says, "That's right little boy, tremble with fear because fear feeds me as well as Chaos Energy."
Just as things looked very bad, a streak of lightning and a Dimension Portal appears out of nowhere. While the lightning appears Rafe and Paige had no idea what it was, Shun thought it was more Chaos Bakugan and Marucho thought that it was help.Marucho is right and someone appears in the Dimension Portal. It happens to be an old friend of the brawlers from Vestal and it is none other than Spectra Phantom. Paige and Rafe wonder who he was, while Marucho reveals that he sent a SOS message to all of the Brawlers' allies which Spectra was the first one to receive.
Spectra then says that the Chaos Bakugan are a disgusting sight and then he says "Let's clean house" by Spectra sending out his new Guardian Bakugan called Darkus Infinity Helios. Also the Brawlers' were surprised that Helios had an attribute change. Spectra explains that Helios' next evolution required an attribute change. Then, Spectra and Helios decimate a massive amount of Chaos Bakugan but however, he gets hit by some Subterra Iron Dragonoid's. In the smoke, Helios took no damage from the attack because Spectra activated Infinity Helios's new FARBAS Ability, and after that Helios beats all of them. Shun and Marucho are impressed, Rafe and Pagie are amazed, Ben, Jack, Robin and Noah are shocked (the last even stating that Helios is "awesome"). Sellon is shown to be fascinated by Helios's power but not to the point of desire. However Anubias is angry. Then with a snap of his finger, Horridian, Bolcanon and Krakenoid jump out from Team Anubias who are in shock and start attacking Infinity Helios. The Brawlers successfully take them down with their brand new BakuNano's that Rafe gave them but Team Sellon's Bakugan come out of nowhere, alongside another bunch of Chaos Bakugan. Then Anubias senses Dan's arrival as he and Drago, arrive back to assist Spectra and the rest of the Brawlers as the chaos continues.
- Titanium Dragonoid
- Infinity Helios
- Iron Dragonoid
- Cyclone Percival
- Flash Ingram
- Infinity Tristar
Mechtogan Titan Seen
- Zenthon Titan (flashback)
- The Brawlers have the addition of Spectra Phantom to complete their attribute circle. This is similar to what happened in Gundalian Invaders where Darkus was the last attribute to join the Brawlers officially (Ren & Linehalt) and in Bakugan Battle Brawlers where Alice got Alpha Hydranoid from Masquerade.
- This is the first time a Vestal brawler from the Resistance has had a major role since Bakugan: New Vestroia.