After discovering this challenge is GDScript, you can decompile to it and recompile it. Modify the client to give you speed, jump, and fly hacks. Make sure you update `player.markers` to have the `FLAG_BOAT` in it so you can trigger the chest to give you the flag. Lastly, walk over to the chest and get it. 
Full writeup: [https://mahaloz.re/tasteless-21-tasteless-shores/](https://mahaloz.re/tasteless-21-tasteless-shores/)