Here are some MHA villain name options based on your description, playing with different aspects of their character:

Emphasizing the Twin/Shared Body Aspect:

• Janus Serpentis: (Janus is the Roman god of beginnings, gates, transitions, time, duality, doorways, passages, frames, and endings. Serpentis is the genitive plural of "serpens," Latin for serpent.) This name highlights their duality and serpentine nature.
• Duos Serpent: Simple, direct, and emphasizes their twin nature and connection to snakes.
• The Conjoined Coil: More descriptive and evocative, focusing on their physical form.
• Bifrost: (From Norse mythology, a rainbow bridge connecting realms.) This suggests a connection between different worlds or aspects of their being.
• Dichotomy: A more abstract name highlighting their split nature.

Emphasizing the Snake/Serpent Aspect:

• Serpens Rex: (Serpent King) A powerful and regal-sounding name.
• Hydra: (Mythological multi-headed serpent) Evokes their dangerous and resilient nature.
• Basiliscus: (King of Serpents) A classic and menacing name.
• Ophidian: (Relating to snakes) A more subtle and sophisticated name.
• Viper's Kiss: A more evocative and slightly less direct name.

Emphasizing their Genius and Power:

• The Serpent's Mind: Highlights their intellectual prowess.
• The Ouroboros Syndicate: (Ouroboros is a serpent eating its own tail, symbolizing infinity and cyclical nature) This suggests a larger organization they might lead.
• Archimedes Serpentis: (Combining a famous genius with their serpentine nature)
• The Enigma: A mysterious and powerful-sounding name.
• Apex Predators: Simple, direct, and highlights their position at the top of the villain food chain.

Combining Aspects:

• Janus, the Ouroboros: Combines the duality and the cyclical nature.
• Duos Basiliscus: Combines the twin aspect with a powerful snake name.
• The Conjoined Hydra: Combines the physical form with the multi-headed serpent.
• Serpens Rex, Dichotomy: Combines the powerful snake name with the duality.

More Abstract/Evocative Names:

• Whisperscale: Suggests stealth and danger.
• Nightshade: A poisonous and mysterious name.
• Coilwind: Evokes movement and power.
• Venomfang: Direct and menacing.
• Shadowstrike: Suggests their ability to attack from the shadows.

Remember to consider the overall tone and style of your story when making your final choice. The best name will depend on the specific context and feel you want to create.