I've been playing since one of my kids gave me Red in Japanese. Long time. I've got at least one of all the games, and I've had pokerus on every one of them. I thought for a long time all carts have it, because all of mine have.
On the other hand, I've only had, in all that time 2 non-game shinies -- and such cool ones -- a tentacool
and a MAGICARP
And the worst part with the magicarp was one of my cousins EVO'd it.
I was so mad. Commonest in-game shiny ever. Duh.