Ruyi jingu bang is a very special and magical weapon from ancient Chinese mythology that was used by a famous monkey king named Sun Wukong in his adventures. This weapon was given to him by the dragon king of the Eastern Sea and it is very special because it can change size!
Basically, ruyi jingu bang is a big staff that is very strong and powerful. It is said that it can weigh as much as 17,550 pounds when it is at its biggest size, but it can also shrink down to be as small as a needle. This means that Sun Wukong could easily carry it around when it was small, but when he needed to fight or defend himself, he could make it grow really big and use it to defeat his enemies.
Another cool thing about ruyi jingu bang is that it can also control the water, which means it can create powerful waves and even summon rain. This ability came in handy for Sun Wukong during his adventures because he often had to travel on water or face water-based enemies.
Overall, ruyi jingu bang is a very special and powerful weapon that helped Sun Wukong to become a famous and powerful hero in Chinese mythology.