what you need before the first cast
Fishing needs a pole, bait in your inventory, and enough liquid: 75 connected tiles for water or lava, 50 for honey, 1,001 in the Ocean. Under 300 tiles (200 for honey) you take a power penalty, so 300 is the real target. Shape barely matters: the game measures the top row where the bobber sits and counts straight down, so widening a pool underneath adds nothing and a one tile shaft 75 deep works. Casting works while moving, grappled, or on the surface with Water Walking Boots. Shimmer cancels the cast on contact.
fishing power and the line that snaps
Every bonus collapses into one number. Add the pole, the bait and flat bonuses from gear and potions, then apply multipliers that stack against each other: 1.3x at dawn and dusk, 1.2x in rain, 1.1x under cloud, 1.1x on a full moon. Lake penalties multiply after that, and Chum Buckets add flat at the end, worth eleven, six and three.
Without a High Test Fishing Line or either tackle bag, one reel in seven snaps and loses the catch while still eating the bait. Luck shifts power invisibly, never appearing in the displayed figure, by ten to forty percent either way.
how often you get a bite
A hidden counter fills while the line is out and rolls once it passes 660. That roll succeeds at (75 + fishing power) / 2 percent and caps at 125 power, past which extra power only fills the counter faster. Average wait in seconds is 11 divided by (2.5 + 0.038 times fishing power): eleven seconds bare, about one and a half at 125. Reel timing does not matter: the bobber dips two or three times per bite and any click inside that window lands the same catch.
what decides the catch
Each attempt rolls six quality slots independently, from plentiful up to extremely rare, with odds derived from fishing power and rounded down. At 85 power the extremely rare roll lands about once in 52 attempts. The highest successful roll with something eligible behind it wins, and if nothing in your biome and layer fits that slot the game drops to the next one down without carrying the success along.
Quest fish all sit in the uncommon slot, which is why they turn up steadily. An extremely rare success in water checks a fixed shortlist first: Advanced Combat Techniques, the Dread of the Red Sea, the Frog Leg, the Balloon Pufferfish, the Zephyr Fish. When everything fails you get Trout in the Ocean, Flounder or the rarer Rock Lobster in the Desert, and Bass elsewhere.
biome and height
Height comes from the water surface, not from where you stand, so two pools one layer apart let you fish both without moving. Biome reads your own position, except in the Ocean, where the bobber has to be in the Ocean and above the surface layer. Biomes are checked in priority order, the Desert and Ocean block everything beneath them, and catches limited to pure Forest, Underground or Cavern need no overlap at all.
crates
Crates roll separately, ten percent normally and twenty five with a Crate Potion, which power and luck do not affect. They decide which crate instead: a rare roll gives the local biome crate, very rare or extremely rare a Golden Crate, uncommon an Iron Crate, anything else a Wooden Crate, upgraded once the world flips. Honey gives none. Lava gives only Obsidian or Hellstone Crates. Crates outlive the Angler: a Divine Crate supplies Souls of Light and Crystal Shards with no trip to the Hallow, and Hardmode crates supply ore without breaking an altar.
lava fishing and blood moons
Lava fishing needs one of three things: lava safe bait (Magma Snail, Lavafly, Hell Butterfly), the Hotline Fishing Hook, or the Lavaproof Fishing Hook line. One source works but crawls. Two restart the catch counter at 240 instead of zero and three restart it at 480, most of the way to the threshold, which turns farming a Lava Charm from miserable into reasonable.
During a Blood Moon, roughly one reel in six spawns an enemy instead of a catch, one in three with a Chum Caster, unaffected by power or buckets. In Hardmode the Dreadnautilus takes a tenth of them while the Blood Eel, Hemogoblin Shark, Zombie Merman and Wandering Eye Fish split the rest evenly. A Sonar Potion names the arrival in red a second early. One spawn in five is the Surly Slime until you own one.
running a session
Fish the windows where the multipliers stack, 4:30 to 6:00 AM and 6:00 to 7:30 PM, ideally in rain or under a full moon. Crate Potions last four minutes, so drink one near 3:30 PM: a Blood Moon or an Eye of Cthulhu at 7:30 ends the session anyway. Keep the Truffle Worm out of the top left unless you want Duke Fishron, because bait is consumed from the top left downward and a worm parked there blocks everything behind it.
The rewards consolidate. Three Angler accessories fold into one tackle bag and later into the Lavaproof Tackle Bag, with a spare Angler Earring still stacking on top. Three more fold into the Fish Finder, a required step toward the Shellphone.

