>>36462428I don't remember if you need the ticket or not to get to this point, but this is where you need to be. Surf until you see the gap on the side, go through it until you find the truck. You have to use strength from the Pokemon menu, and this adds Mew's data to the dex.
Here's the legendaries page for unlocking the legends:
https://web.archive.org/web/20180805000019/https://shockslayer.com/legendary-events/ 