The Fisherman's Pocket Guide is an informational accessory that shows your current Fishing Power. This accessory can be received as a reward for completing Fishing quests for the Angler NPC.
It does not have to be equipped to display your fishing power; simply carrying it in your inventory is enough. Additionally, the info it provides will be shared with nearby players on the same team as you.
- If the player has a Truffle Worm, instead of displaying a number, it simply says "Warning!" This is likely so players do not forget they will summon Duke Fishron when going fishing with them.