Bends, mirrors and the pause mark
In the first ponds every koi swims straight to the edge it faces. Then, still inside Stillwater, some begin to bend. By Riptide some also pause. These three behaviours are the whole grammar of the pond, and each has a mark on the koi’s head that tells you what it will do.
Straight koi
A straight koi swims in the direction it faces until it reaches the pond edge, and it leaves the pond there. Its path is the line of cells from its nose to the edge. If every cell in that line is empty of other koi, it can go. This is the opening rule and it never changes; everything else is built on top of it.
Bend koi
A bend koi carries a small curved arrow on its head. It swims forward until it reaches the pond edge, turns — right, if the arrow curves right — and swims along the edge to leave through the next edge. Its path is therefore an L: the straight run, then the run along the edge. Both legs must be clear.
Bends enter early on purpose. Their share of the pond climbs from none at the very start of Stillwater to about a third of the koi by the end of the tier, so the signature idea of the game — that a koi’s exit is not always the edge in front of it — shows up in the first session rather than after an hour. The practical rule: when you see the curved arrow, trace the L with your eye before you tap. The most common early mistake is a clear straight leg and a blocked corner.
Mirrors
A mirror is simply a bend that curves left. It appears in Currents, and from then on the ponds mix right bends and left bends. There is nothing new to learn mechanically; what changes is that you can no longer assume the direction of the turn, and two koi on the same row that bend opposite ways have paths that cross. The arrow tells you. Read it every time, especially on a Karasu, whose dark head makes the arrow the hardest to see.
The pause mark
Some koi from Watchers onward carry a pause mark between the eyes, aligned with the way they face. A pause koi swims to its corner and stops there, mid-turn, and waits. When it has turned and is waiting, the mark becomes an arrow pointing the way it will go. Tap it again and it finishes its path along the edge.
This does two things to a pond. First, a waiting koi occupies its corner cell, so any other koi whose path runs through that cell is blocked until you send the paused one on. Second, the pause splits the koi’s crossing of a predator’s lane into two moments: it may cross one lane on the way to the corner and a different lane on the way out, and the two lanes have two different clocks. A pause koi is therefore the one to plan carefully around a predator: park it at the corner while a lane is red, then release it as the lane turns orange.
Planning a pond
Put the three together and a pond becomes a small ordering problem. Straight koi are free moves once their line is clear. Bends need a clear corner, which often means moving a straight koi out of the corner first. Pause koi are corners you can hold. A good habit for a crowded board is to find the koi nearest the edges first — they are the ones with the shortest paths — and clear them outward, opening lanes for the ones behind.
The Hint helper (20 coins) shows one koi that can move now; Undo (15 coins) takes back a tap. Both are cheap on purpose: the game would rather you keep drifting than stare. But the pond is designed so that the read is always possible without them, and by the end of Watchers most players find they are not using them at all.
One rule, many ponds
None of the three behaviours changes the rule that a koi leaves only when its whole path is clear. They change what “whole path” means: a line, an L, or an L with a stop in it. The tiers add koi, predators and speed on top, but a thousand ponds later the thing you are doing is still tracing a path with your eye before you tap. That is why the game can stay calm while getting hard.