Umm there is an ending, this is how you get to it.

First of all you must have a full set of each armor in your inventory, and have the mlten set equipped. Also, you must have rocket boots, muramasa, flamelash, and a blade of grass in your inventory.

After you have collected the above, and have nothing else in your inventory, talk to the guide again. He will say something like, "I sense an even darker presence coming from the dungeon."

Now its exploring time. You must search the walls of a dungeon for an opening that was not there before. It is easy to spot because the blocks will be a different color, usuallya sort of reddish gold. Enter and follow this passage, fighting monsters that do not spawn anywhere else. You will then enter a room where a short cut scene plays, showing the guide saying something like, "You're finnally here!"

Spoilers

He will then transform into a huge fiery monster. Flame weapons will not hurt him, and your blade of grass will be destroyed if it touches him. Use your rocket boots to fly around him and hit his weak points. They are easily noticed

After you burn his health halfway down. He will reveal his other form and push you into a dark portal he creates. You will appear at your spawn point, and a few seconds later so will he. This form is a lot smaller, and will start destroying any blocks you have created if you do not constantly hit him. None of your weapons will do much damage, until you hit him with the muramasa. This will show muramasa's true form. After a few hits, your soul will be ripped from your body, allowing you to fly and be invulnerable, but there's a catch, you must defend your physical body.

After a while, he will stop fighting you, offering an escape from this island. If you accept, congrats you beat the game! If not, you can deal the killing blow and receive one of three extremely rare items