Fishing is done at specific spots, not everywhere
As Sonic zooms into a semi open-world adventure with Sonic Frontiers, the “greatest hits” of the genre comes with it: which includes a fishing minigame. But given the historical significance (depending on who you ask) of Big the Cat, you could argue it actually fits here.
Here’s a quick guide on how to approach fishing in the game.
In Sonic Frontiers, fishing has to be done at fish icons on the map
So you can’t just get a special fishing rod item and fish anywhere on the map: but by that same token, the minigame doesn’t require you to get a unique fishing rod either. You’ll come across specific locations where you can initiate a minigame, hosted by Big the Cat. It’ll be denoted by a fish icon on the map.
Once you’re in, Big will actually give you a quick tutorial on the process, which costs purple fishing coins (which you’ll find in the game world). Catching fish will grant you green “treasure tokens,” which are used on items in Big’s shop (more on that later).
The actual fishing minigame is pretty easy – just tap when the white circle is in the red circle
After casting in an area with fish shadows in the water: all you need to do is press the button on the prompt (X on PlayStation) when the white circle enters the red circle. That’s it. Be prepared though, because some fish put up a bigger fight, and require two circle button presses in quick succession. Caught fish will generally convert directly into treasure tokens: and you’ll rinse and repeat until you’ve earned enough to buy what you want.
Instead of fish, there’s a chance you can randomly pull out scrolls. These unlock fast travel on the island you’re on (read: there are multiple sandboxes/islands) to the Elder or Hermit Kocos (NPCs) of that particular island.
The rewards are actually pretty good
Once you earn a few treasure tokens, you can buy stuff based on a few options in Big’s shop. Take note of the little numbers above the actual shop selection. That’s your current count of everything in that area, which could influence what you actually buy.
If you’re looking for progression and aren’t having many issues with the game’s difficulty level: choosing Portal Gears and Chaos Emerald Vault Keys will get you further through the story. Egg Memos are kind of like BioShock audio logs, and give you extra story background on Eggman. I would recommend never buying memory tokens, as they’re one of the most common collectibles in the game.