Skeletons are deceased humans made of skulls and decayed old bones. They are controlled by the wearer of the Skeleton Ring
At some point the skeletons were alive and real people. When they died they became part of the undead skeleton army through unknown means. Whoever wears the Skeleton Ring controls the army.
They first appeared at the end of the episode No. When Puss, Dulcinea, Artephius, and San Lorenzo figured out the that Fartholomew (disguised as Sino) is a fake. Fartholomew used the skeleton ring to summon the undead army. Puss and the San Lorenzans battled the army and destroyed it but Fartholomew fixed and reawakened them. All was lost until Puss' old black cat friends, The Guild of Darkness came to their aid. With support from them Puss disarmed Fartholomew from the skeleton ring and sent it blasting, which caused the skeletons to fall apart and deactivate. The black cats went in search for the ring.
At some point they gave the ring to Captain Two-Eyed Alonso. Which unknown to him controlled the Skeleton Army, but known to his parrot pet Bonky that stole it, then flew away and betrayed Alonso.
When Puss met Alonso and his pirate crew to help him find the treasure he was seeking in exchange for the Crown of Souls. Alonso explain that the Skeletons stole the map by the orders of their leader(which later turned out to be Bonky). Later, the skeletons attacked Alonso's ship, but with Puss' help they junked the skeletons and stole the map back.
A while later the skeletons tracked Puss, Alonso, and his pirates to an uninhabited island. Bonky reveals himself as their leader and explains why he left Alonso. He then has his skeleton army burn Puss and the pirates alive. However they start singing which get the skeletons to dance. They break free, but Puss steals the skeleton ring from Bonky and gets control of the army. The Army captures Bonky and brings the treasure to the Queen James(Captain Alonso's ship). Alonso had Bonky walk the plank, but he flies away a swears that he will return. Puss then gets the Crown of Souls and the skeletons get a free life in San Lorenzo.
In the next episode the citizens of San Lorenzo get freighted by the skeletons. Pajuna refuses to allow them in the cantina. Later at night the skeletons were doing sneaky activates. Eames when to spy on them, when he thought they we building a weapon of doom. Puss was refusing to believe that the skeletons were doing something evil, but agreed to spy on them. He then thought that the skeletons were building a weapon of doom, so he and the San Lorenzans tried to stop them but Uli attacked San Lorenzo with a Magical bow from the Treasure House. The skeletons rushed to save Puss and the people of San Lorenzo. The the Skeletons displayed their special powers and trapped Uli in a bone cage. Uli was given a chance to become good by Dulcinea which he accepted. The skeletons showed that they were building a statue of friendship and all of them danced and celebrated.
A while later they appeared when the misguided Uli tried to teach the Thieves to be good, but things went out of hand. Thieves were taken the rhymes they were taught with and harassed San Lorenzo and the skeletons. Later Uli gave up teaching them and the thieves started terrorising the city. Pus sent them running and everyone(including skeletons)were cheering in relief.
When the bloodwolf return everyone was running in fear of him and his flying wolf aviators. The people managed to fight up against him with the help of Puss, Dulcinea and the Senior Puss Squad. When the bloodwolf was banished to the Realm of Shades with Uli, everyone was celebrated thei victory.