If you don’t have Gallant Thief, another option is to change your going-second plan pretty significantly.
When you have Gallant Thief, the main game plan is usually to pair it with draw-based hand traps and use Gallant Thief to break their board.
But you can also go in a different direction by playing more negation-based hand traps and focusing on stopping the opponent’s combo before they can establish their board.
I’ve attached a list as an example.
I tried this kind of build in Singles and honestly liked how it played, so hopefully it gives you some ideas!