Ultimate Weapon is the 50th episode of Bakugan: New Vestroia. It aired on May 8, 2010.
Hydron discovers that his fellow prisoner is none other than Gus, who was presumed dead in Avenging Spectra. Meanwhile, Runo, Julie and Mira prepare a cake for Keith to officially celebrate him joining the Resistance. However, Keith's mind lingers elsewhere, something that Mira notices, but he denies. Dan suggests that instead of waiting for King Zenoheld's attack, they should storm the palace. Keith however, is too impatient and takes his Vestal Destroyer to the Mother Palace on his own. A battle quickly ensues, and Gus flees from the jail when Spectra needs his help, by tricking Hydron into battling so their Bakugan can free them from their cells. Then, Gus leaves to help him and Helios, while Hydron is left on his own. King Zenoheld nearly defeats him, but luckily, Gus arrives in the nick of time, shocking Spectra who's happy finding out that he survived. The two then battle together, giving them the initial upper hand against Zenoheld who then starts to overpower them. At this point in the battle, Professor Clay informs Zenoheld that the Alternative System, a giant airship modeled after Farbros is complete and as a first objective it's target is Spectra and Helios for a test fire. The blast sends Spectra's ship flying and takes a huge chunk out of a small planetoid, with him and Gus just barely escaping the impact. Farbros links with the Alternative, and Zenoheld declares that his quest for intergalactic domination has begun.
- The Resistance has a party welcoming Keith and Helios, then decides to storm the Mother Palace in the morning.
- Keith becomes restless and decides to leave in the middle of the night to storm the Mother Palace alone.
- Keith challenges Zenoheld to a battle.
- Gus tricks Hydron into battling him, thus freeing both him and Hydron from the prison.
- Gus joins Spectra's battle with Zenoheld, revealing that he survived his previous encounter with Zenoheld.
- Zenoheld and Clay reveal that the Alternative has already been completed.
- Keith forms Maxus Helios, but all of the Bakugan that make it up (other than Helios) are destroyed by Farbros.
- The Alternative fires for the first time, destroying most of the palace and decimating a small moon nearby.
- Hydron and Dryoid flee the palace as the Alternative fires.
- The Alternative is revealed to be able to link with Farbros.
- Assail Farbros
- Helios MK2
- Maxus Helios MK2
- Rex Vulcan
- Helix Dragonoid
- Minx Elfin
- Saint Nemus
- Master Ingram
- Magma Wilda
- Knight Percival
- Blade Tigrerra
- Hammer Gorem
Battle Gear Seen
- This is the one of two episodes to have the same name in both English and Japanese, the other being Ambush.
- The scene where Runo and Julie unveil the cake to Spectra and the Battle Brawlers is extended in the Japanese version, showing the Resistance Bakugan dancing on the cake. It was most likely cut in the English broadcast due to time restraints.
- The dancing mimics the Bakugan dance seen in the second Japanese ending.