This level introduces the low-gravity mechanic. Mario jumps higher and falls slower, which can take some getting used to. You'll encounter alien enemies (Space Goombas) and flying saucers (UFOs) that shoot projectiles. There are also sections with moving asteroid platforms. A Super Mushroom is usually available early on. A hidden Carrot is extremely valuable here, as Bunny Mario's float combined with low gravity gives you incredible air control, making precise landings much easier. Look for it in a block above a small pit.
Gravity Adjustment: Practice your jumps in the low gravity. It's easy to overshoot platforms or fall into pits if you're not careful. Use short taps of the A button for smaller jumps and hold it for higher ones.