Super mario

you have to beat the boss as mini mario at the end of world 2 and 5

You need to beat the bosses of Worlds 2 and 5 as mini Mario.

When you beat them normally, you should notice as Mario runs into the next room, there is a tiny path under the ground. Those paths are to Worlds 4 and 7, and only mini Mario can fit in there.

So when you fight the bosses, either have a mini mushroom in reserve or go into the fight as mini Mario, then in order to hurt the bosses, instead of regular jumps, you have to do a ground pound on them. Three ground pounds will do it, but make sure you are mini Mario at least on the last attack, and then you're off to World 4 and/or 7!

You need to get the mini mushroom's in each castle and beat the boss of each castle while staying mini for both world 4 and 7 to be unlocked.

just beat the last boss in world 2 (sand worm i think) using the mushroom that makes you tiny. Do the same thing in world 5 to unlock world 7.

for world 4and7 you have to be mini on world 2 then defet the boss on that like mini and there is world 4 on the map (do the same on world 5 for 7)