Looking at the website, I could see a text box and submit button. I tried to submit random stuff but I got incorrect. Thus, I tried to look at the source code, then I got a js file but it's already obfuscated -> I tried to deobfuscate it by using the only tool as you can see in the result below.
After analyzing the code, basically, the text box takes each character of the user's flag and then submits it to WebAssembly using copy_char then calls check_flag to see if the flag is correct. From here, I thought I have to dive deep into WebAssembly to get the flag. From
From the JS code above, I could see let leftBranch = await fetch(findMiddlePosition('./JIFxzHyW8W'));-> I tried to get the WebAssembly code from mercury.picoctf.net:1896/JIFxzHyW8W then open it as a text file in vscode -> got the flag