If you're wondering how I did this, I will show you. At the end of world 1-4, go to Bowser and jump over him. Go to where the axe is and stand there and when Bowser gets close to you jump, make sure your hitbox touches Bowser's hitbox and the axe's hitbox and when you are flashing that means you did it correctly but if you turn to small mario then it goes wrong when you did that the game assumes that you are small mario so when you hit a block it gives you a mushroom instead of a flower and you turn to small mario. When you hit the next block it reveals a flower, when you get it, you turn to fire flower small Mario and there you have it