Wonder Boy in Monster World

The Legendary equipment is the absolute best equipment you can get.
The Legend Sword, Legend Shield, Legend Armour and Legend Boots make up the equipment.
The Legend Sword is story related and cannot be missed. You’ll receive it from the blacksmith in the dragon village by giving him 2 items to forge the sword with.

You can find the other equipment in the Nightmare Castle, here is where you can find them:

Legendary Boots - When you are on the trolley track, jump down past the trolley, and walk to the left. Kill the ghosts, and drop down at the end. Go right until you get bounced onto a platform with a chest on it. The legendary boots are inside the chest.

Legendary Armour - Next, go back to the top and ride on the trolley this time. Stay on it all the way down, and make sure you duck under the spikes. When you reach the bottom left, jump up onto the platform that you wouldn’t be able to reach if you weren’t on the trolley. When you are on the platform, go up the chain. Jump onto the rope on the ceiling, and jump onto the other one to avoid the spikes. Fall down the pit you were in the middle of going over. When you‘re down there, open the chest to find yourself some legendary armour.

Legendary Shield - When you come to the place where there is two ropes, make sure you have thunder magic equipped. Then go up the second one and when get to the middle, use your thunder magic. This will kill all the tomatoes. Ride the rope down, and then get on the first rope. When you get to the top, you will see a chest. Open it for the Legendary Shield.