Saffron City was a playable stage in the original Super Smash Bros., but did not appear in the sequel, Super Smash Bros. Melee. It was one of three stages that did not have a similar stage to it in Melee. Although some people say that Fourside is similar, there are far too many differences.
Some of the Pokemon that appeared from the door in Saffron City, however, continued into Super Smash Bros. Melee, including Venusaur, Chansey, and Electrode. it is also worth noting that although Porygon did not return, its evolved form, Porygon 2, did appear as a Poke Ball Pokemon.
This stage is allowed in standard tournaments save for a few situations.
Lay of the Land
Saffron City has a main platform, and a tiny one above the Pokemon door. To the right of this is a narrow platform. To the left of the main platform are two elevators (moving platforms); between these and slightly lower than the others is yet another narrow platform.