Harpie's Pet Dragon + Bolt Escargot → Twin-headed Thunder Dragon

Harpie's Pet Dragon + Bolt Penguin → Twin-headed Thunder Dragon

Harpie's Pet Dragon + The Immortal of Thunder → Twin-headed Thunder Dragon

Harpie's Pet Dragon + Electric Snake → Twin-headed Thunder Dragon

Harpie's Pet Dragon + Mega Thunderball → Twin-headed Thunder Dragon

Harpie's Pet Dragon + Electric Lizard → Twin-headed Thunder Dragon

Metal Dragon + Thunder Dragon → Twin-headed Thunder Dragon

Metal Dragon + Kaminari Attack → Twin-headed Thunder Dragon

Metal Dragon + Tripwire Beast → Twin-headed Thunder Dragon

Metal Dragon + Bolt Escargot → Twin-headed Thunder Dragon

Metal Dragon + Bolt Penguin → Twin-headed Thunder Dragon

Metal Dragon + The Immortal of Thunder → Twin-headed Thunder Dragon