Have a trick, some more tricks, etc. up your sleeve
Definition 1 of 1
Pro Tip 1/3Hidden Advantage
Use it to describe a concealed skill or resource that one can draw upon when needed. 
Despite being underestimated, she had a trick up her sleeve during the debate.
Pro Tip 2/3Strategy Reveal
Mention it when someone reveals a clever strategy to address a problem that wasn’t apparent before. 
When we thought all was lost, our coach pulled a trick from his sleeve.
Pro Tip 3/3Surprise Element
Highlight unexpected solutions or surprise elements in a story or conversation. 
The magician had one more trick up his sleeve, leaving the audience in awe.