Build a coinflip game, where the user can connect their wallet and then flip a coin on the screen.
User can select how much tokens from their wallet (SOL, ETH or BTC) they want to risk, and also select a side.
If it lands on the side that they chose, they get double their tokens back, if it’s the wrong side, they get nothing.
To get testing tokens use a ‘faucet’
You should deploy a simple smart contract so that the users wallet actually loses/gains tokens.
Show the transaction of the user gaining / losing funds on etherscan, solscan, etc