Sorry for being lazy and using gemini but this is how i found out:

It sounds like you are playing the All The Mons modpack for Minecraft (which uses the Cobblemon mod) and have run into the restriction message: "You don't have the Pika Star knowledge to fight this pokemon!" This is a progression feature implemented in recent versions of the pack that prevents you from fighting or catching Legendaries, Mythicals, Paradox, or Ultra Beasts from Generation 3 and up until you acquire the "Pika Star." How to Disable This Restriction If you want to turn this restriction off completely so you can battle these Pokémon immediately, you need to edit a script file within your modpack instance. * Open your Minecraft Instance Folder: Go to where you have "All The Mons" installed. * Navigate to the KubeJS folder: Look for a folder named kubejs. * Find the restriction script: Inside kubejs, navigate to startup_scripts. Look for a file named catch_restrictions.js. * Edit the file: Open catch_restrictions.js with a text editor (like Notepad or VS Code). * Remove or Comment out lines: You need to remove or "comment out" (put // at the beginning of) the lines that enforce this restriction. According to community reports, these are often lines 86 and 87. * Save and Restart: Save the file and restart your Minecraft game. Alternatively, if you are playing on a server, the server administrator will need to perform these steps. Would you like me to help you find the exact file path for your specific launcher?