Continuing with my sonas, here's my pokesona, Dei'Gon the zweilous. The right head is Dei and the left one is Gon.

I feel it's worth mentioning that the way I see the hydreigon line to work is that upon evolving, Deino's head splits into two, each with one half of the brain, wich is why each of zweilous heads only has one nostril, and when it evolves, the heads fuse back together into one while the forelimbs become pseudo-heads. I just don't like the concept so many people have that when zweilous evolves one of the heads die, or that a new one grows and the other two lose their brains. Besides, in my opinion it's pretty clear it works this way, wich is why they put those details like zweilous only having one nostril on each head or hydreigon's secundary heads having an elbow on the "neck".