>>35813404I'll try but fair warning, this is nothing but a shitpost.
Haunter gains Kadabras full body and tail.
Kadabra loses most of his lower body (that giant tail) and gains two things in his hand (spoons)
They both have the pointy cone ears.
The real connection is they made Machoke and Graveler's evolutions based on trading them with each other but then decided that restricting you to only trading one for the other was a bad idea so they dropped that, and then the next trade evolutions weren't designed with that in mind. Gengar was Clefable as a shadow and Alakazam was Kadabra with an extra spoon.