There is always Night Master being threat to Woo Foo, they have changed after hundreds of years
Eradicus was the original Night Master, and responsible for eliminating Ti and Chai and destroying Woo Foo. He had a massive army made of stone, and took over the world; however, he was later destroyed by unknown means.
Snake Lady was the second Night Master. She had a very long neck and possesed a whip. Her abilities are unknown, though she might be the reason behind the destruction of the great Woo Foo masters in Yo's childhood.. This might imply that she was stronger than the third Night Master. Other than that, little is known about her, and she has yet to make her official debut in Yin Yang Yo!.
Billed as a "Dark Overlord In An Evil Class All By Himself", the Night Master is a very powerful and dangerous foe who was responsible for the near extinction of Woo Foo by eliminating all of the Woo Foo knights except for Master Yo. The Sensei managed to turn Night Master's army to stone and sent him into hiding for a hundred years until he tricked Yin and Yang into using Woo Foo in order to free his army. The Night Master appears to be a demonic sorcerer bat of some description and has a liking for gothically ostentatious outfits. He frequently communicates with his lackeys by using a hologram. He is seen in Shadowcluck running a garage sale. His real name is unknown.
He became the new Night Master in "Deja Foo," calling himself the Night Mooster. He became regular Ultimoose again after Yang reversed time, found the Amnesulet first, and was aided by the other villains to defeat him.
Once again Eradicus begins attempts for destroying Woo Foo after Welcome to the Dark Tomorrow, though, he starts using modern technology but still being confused since technology didn't existed in his original century, still he uses modern plans such as Eradicorp. He was defeated in Yin Yang Who? by being thrown to the side of the Old Night Master's Lair.
Ferocitus is the current Night Master after the defeat of Eradicus, but Yin, Yang and Yo were ready to fight. He was only seen in Yin Yang Who?. He has been speculated to replace the previous Night Masters as the primary antagonist in Yin Yang Yo!s upcoming third season.