Doom Leonidas is a Darkus Bakugan and the evolution of Valentin's Omega Leonidas. He evolved after being fueled by the anger he gained when he learned that the Bakugan on New Vestroia were captured by the Vestals.
The evolved form of Valentin's Omega Leonidas, Doom Leonidas has more power than his previous form. He gains a lust for vengeance against the Vestals for capturing his fellow Bakugan on New Vestroia.
Bakugan: Helstara's Rise Arc 1
In A Grand Return, Valentin is walking in a park when a portal opens in front of him. He is sucked into the portal and meets with Leonidas, who had evolved prior to this event. The two are happy to see each other again, only when Valentin realizes that he is on New Vestroia, he asks what happened to the Bakugan and Leonidas's look of happiness becomes one of rage. Leonidas tells them that they have been captured by a sapient species called the Vestals. He explains that they certain crystals that make Bakugan revert to Ball Form, even in on the Bakugan's home world and paradise. However, Leonidas is in Warrior Form, which results in Valentin asking him why he isn't in Ball Form as well. Leonidas that hypothesizes that it is most likely because he was born in the Doom Dimension, where crystals such as those of the Vestals might not be able to hold sway. Valentin then uses new acrobatic abilities he honed before their encounter and jumps all the way onto Leonidas's left shoulder, a habit that will occur later on in their adventures. The two then fly off to find the first crystal.
Later, in Proven Shadow, Leonidas and Valentin discover a set of ruins in a long-deserted section of New Vestroia. There, Valentin finds a large carving that shows the six Attribute Symbols plus six more symbols, which are secretly referring to the Six Lost Attributes of Helstara. Leonidas stares at the symbols, stating that they look peculiar. After that, the two exit the ruins, only to be encountered by a figure who introduces himself as Shadow Prove. Despite Shadow having three Bakugan and Valentin one, Leonidas is still stronger. Shadow sends out a Darkus Sylthee, a Bakugan that Valentin nor Leonidas have ever seen before. Shadow then sends out a Darkus Anchorsaur and a Darkus Hammersaur. As the battle ensues, Leonidas reveals his new powers as Doom Leonidas. In the end, Leonidas and Valentin beat Shadow with no Abilities, for Valentin did not have a Gauntlet. Shadow then teleports away, telling the two that he'll be back for revenge. Valentin then states that he needs the device that Shadow had in order to use Bakugan Ability Cards - referring to his Gauntlet. Leonidas then reveals that he has one of those, and says that he had stolen it from a Vestal base in case. Valentin then questions why Leonidas did not tell this to him earlier, but Leonidas says that the place where he hid the Gaunlet was too far to reach in time when they had encountered Shadow. The two then fly off in order to reach the Gauntlet's hiding place.
- Doom Phaser: Gives 400 Gs to Doom Leonidas.
- Vortex Fiery Darkus: Gives 200 Gs to Doom Leonidas and takes 400 Gs from the opponent.
- Vortex Shadow Pyrus: Gives 300 Gs to Doom Leonidas and takes 300 Gs from the opponent.
- Bakugan: Helstara's Rise Arc 1/Bakugan: New Vestroia