I received an email last February:
hi when i was looking at a pokemon site the other day i saw a pokemon thatts a pikachu and a sandshrrew together and they said it was real. is it real
It's really embarrassing how long it's taken me to get to replying to this, but my life has been really busy and I've been distracted by the Glitch Cities. But I think you deserve your answer
First you have to go to Bill's house. You have to have a full Pokedex including Mew. And you have to have finished Bill's quest line which is quite time consuming ;(
But with these requirements met he will let you use his computer where he is testing his Cell Fusion System.
I tried 3 fusions:
Pikachu + Sandshrew
Magmar + Parasect
Slowpoke + Lickitung
It gives you a popup showing you what the fusion looks like, but then it closes out. Then your Pokemon are just gone and I don't know where they go. They aren't accessible from the PC, Bill doesn't say anything new, etc. Well I lost 6 Pokemon this way because I got excited and now I'm really ticked off because that was my Pokemon Yellow Pikachu.
I don't even care about the fusions anymore, I've been trying to ask Supernerd how to get my Pikachu back but I think I'm freaking her out. So that's all I got for right now I'll get back to you if I can figure this one out. I hope you like the pictures anyway.