After you defeat Croco, you get a bomb that you can use to go farther into the Moleville Mines.
How to Get Here
After you explore the first part of the Moleville Mines, you will battle Croco and get a bomb. You can use this to reach the second area of the mines.
After the Croco Battle
After you get a bomb from Croco, go northwest as far as you can go. Then, depending on which room you end up in, you can either go northeast or southwest. Do so, then go northwest to the next room. From there, go northeast, and go to the eastern part of the room to find Pa'Mole. Talk to him to open the way. Then you can go northeast to the next part of the mines.
There are two paths to the northeast. You should jump up the wooden crates and go through the upper of the two northeast doors. Then you can go northeast to a treasure box and hit it to get an invincibility star. Bombs will fly at you while the star is in effect, so run into them to get more rewards. At the same time, go northeast and through the upper exit.
If you ended up on the lower level, jump up the crates. From the upper level, go through the southeast exit.
Jump up the crates here and hit the chest to get some coins. Then go northeast.
There are Bob-ombs on the tracks to the northwest. If you want to avoid them, wait for them to be moving toward you, then you can try to run and jump over them. After you get past them, ignore the chest and save block and go northeast where you can see another chest. This one is difficult to reach. Jump onto the stack of two wooden crates, then make a running jump to hit the chest and get a Fire Flower. Then go back to the chest and save block. This way, you start by getting a Fire Flower to increase your FP, then you fill up your FP with the Mushroom in the chest near the save block. Use the save block, then go northeast to the next area.
You might want to equip the Fearless Pin on a party member if you have it.
There are some Bob-ombs wandering around the room, and there is a purple monster in the northeast part of the room. The purple monster throws tiny bombs around the room that will knock you a short distance back if they explode on you. Don't approach the purple monster from the front or it will knock you back to the save block in the previous room. Approach the purple monster from the back and there will be a cutscene, and then you will have to battle Punchinello.