The double-headed Nillious main motive in brawls is to kill - not to win. He does not like fighting as a team with his partner, Nillious is out to satisfy only himself. He likes to go rogue. Each head has its own personality & ability. Untamable & vicious, Magnus has his hands full keeping Nillious in line.
In the show, more specifically the shorts, it is noticeable that the heads have their own personalities if you squint. The left head (orange eyed one) seems to be a bit less maniacle, and slightly more timid, than the right head (green eyed one). The right head (green eyed one) also seems to be the one that wants to pick a fight more often. In all honesty, both heads are quite mischivous, as they obviously enjoy to prank, irritate, or mock others- their favorite subject being Drago. The right head (green eyed one) has even been seen mocking Magnus, to the best of his ability, which the left head (orange eyed one) enjoyed- this was in the short released only in Japan so far.
As Titan Nillious, Nova seems to be more belligerent and unpredictable than Shadow, as he seems to attack mainly while Shadow defends and has even shown to try and charge into Dan until Magnus demanded him to stop, trying to break free Tiko's control.
Pact of Darkness
Darkus Blast (Dark Blast)
Reflection: Reflects an opponent's attack.
Nillious bears a strong resemblance to Dual Hydranoid due to both being two-headed dragon Bakugan.
Additionally, theirowners also wore a mask & were Darkus Brawlers.
Nillious' left head has one horn and green eyes, while his right head has two horn and orange eyes.