"Card up sleeves" is an idiomatic expression that refers to having a secret plan or advantage that one can use to gain an advantage in a situation. There are various synonyms for this phrase, including "ace in the hole," "trick up one's sleeve," or "hidden agenda." Another similar phrase is "secret weapon," which implies that someone has a powerful tool or tactic that they can use to achieve their goals. Some may use slang terms like "joker in the deck" or "wildcard" to describe a hidden advantage. Whatever the phrase, it's important to remember that having an extra move in reserve can often turn the tide of any game or competition.