We actually had a dual hero Concept Design Contest that happened a few months ago: CDC #8 - Double Trouble
Other than those, here is a list of the concepts that were passed around:
- Twin Emperors
- Twin Val’kyr
- Han and Horner
- Falric and Marwyn
- Skarvald and Dalronn
- Aysa and Ji
- Thassarian and Koltira
- Theralion and Valiona
- Twin Mogu
- Fuegen and Stalagg
- Rakanishu and Bishibob
- Clever Ashyo and Ken-Ken
- Millhouse and Millificent Manastorm
- Lora Crowley and Tess Greymane
- Jadefire Masters
- Onyxia and Nefarion
- Rastakhan (or Talanji) and Bwonsamdi
- Akama and his Shade
- Will of the Emporer
- Rotface and Festergut
- Sully and Amber
- Archon
- Durotan and Draka
- Alleria and Turalyon