Just so you know, this is not a game crossover (although that would be a splendid idea). It's a merchandising crossover.
Compared to the original Japanese Super Mario Bros. box art, with the Pokemon substituting for:
- Squirtle as Koopa Troopa
- Qwilfish as Cheep Cheep
- Psyduck as Hammer Bro.
- Ferroseed as Spiny
- Landorus as Lakitu
- Shroomish as Goomba
- Wartortle as Koopa Paratroopa
- Beldum as Bullet Bill
- Inkay as Blooper
- Flabebe as a flower
- Foongus as Toad
- Diancie as Princess Peach
- Blastoise as Bowser
- and of course, Pikachu as Mario
Interesting that representation is found in 5 out of 6 generations, with the exception of Generation 4.
There are some interesting merchandise found here, including trading cards and stuffed toys: http://nintendoeverything.com/mario-and-pokemon-crossover-merchandise-announced-for-japan/
Thanks for reading.