Thunder Dragon + Thunder Dragon → Twin-headed Thunder Dragon

Thunder Dragon + Stone D. → Twin-headed Thunder Dragon

Thunder Dragon + Kaiser Dragon → Twin-headed Thunder Dragon

Thunder Dragon + Aqua Dragon → Twin-headed Thunder Dragon

Thunder Dragon + Sea King Dragon → Twin-headed Thunder Dragon

Thunder Dragon + Spike Seadra → Twin-headed Thunder Dragon

Thunder Dragon + Kaminari Attack → Twin-headed Thunder Dragon

Thunder Dragon + Tripwire Beast → Twin-headed Thunder Dragon

Thunder Dragon + Bolt Escargot → Twin-headed Thunder Dragon

Thunder Dragon + Bolt Penguin → Twin-headed Thunder Dragon

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

Thunder Dragon + Electric Snake → Twin-headed Thunder Dragon