I'm sorry. I'm going through some stuff.
I was also thinking about my sis. How we played games together when we were younger. I miss that more than anything. I wonder if I can ever find anyone that I could do that with. I have some memories wrapped up in this game. I loved that little train. The car! Oh, that submarine. :-) Baby Mario's Invincible music!
I know to some of you, this was just a great game. But for me, there's a lot of emotion attached to it. Oh, just thinking about how the light flickered through the trees as you ran along. The many myriads of creatures that inhabited the island.
In my mind, I haven't seen a game to match it.
Oh, the world question. I don't know. There are those things that I mentioned… I do like world 4, because of the one level (1, 2?) where Mario can be invinsible for as long as he likes. And you can listen to that music for as long as you want. I also thought playing with the Baseball boys was cool. I dislike those mice, though, as they'll take Yoshi's eggs without you knowing it.
My sister liked/hated world 3 because of those monkeys. They're really cute and fun to play with. Ever tried drowning one? (They're unconscious when Yoshi spits them out, right? Toss them in the water, and they're like "WHOAH!") Oh, watching those little frogs (they're scenery, yet they interact with Yoshi—So Cool!
I'm sure this is how Yoshi and Mario developed that close bond between them.
Please excuse all my mushy stuff.