When you arrive underground in Land's End there will be two stars, one in the treasure box at the save point, and another that can be bought for 400 coins. Get the first star and you should have enough time to knock everyone out up until you fall down the hole with the Gecko creatures. Look for the man behind the boxes and buy a Star. You should also knock out all the creatures. Whichever three party members you use, un-equip them to the point where they have absolutely nothing. Fight Belome and intentionally die. This will return you to the save point where you can get two new Stars. Repeat this process as needed to gain levels. It is recommended that Mario is equipped with the Exp. Booster (found in Seaside Town, Elder's House, upstairs, 22 frog coins) so he benefits the most.