He is an exact clone of Puss (physically) though he wears a paper hat instead of Puss's hat.
Puss Dos is a simple cat, enjoying the simple things in life like hugging and lunch time.
He is very dumb, frequently tripping on nothing and running into things. He lacks Puss in Boots' natural grace and skill and instead makes up for it in loyalty and enthusiasm. He's chaotic in nature, often going off and doing his own thing and lacks any common sense.
After accidentally promising to ride for two teams in the town's horse race, Puss in Boots, with the aid of Artephius, creates a duplicate of himself to ride in his place. After the spell is cast, Puss Dos is revealed to be a not-so-accurate copy of Puss, being clumsy and much dumber than the original.
During a brief training period before the race, its revealed just how different Puss Dos is from the original and Puss in Boots grows impatient with each failed attempt at coaching his clone. On the day of the race, in a surprising twist of fate, Puss Dos ends up winning the race with his horse crossing the finish line before Puss's.
Later in the series Puss Dos continued to make brief cameos, often having only one or two lines of dialogue before disappearing again.
There's nothing wrong about him, he is just dumb, but still perfect in his ways.