This post was originally written in January 2018. At the time the game was still called Hook, Line and Thinker

One of my design goals with this game is accessibility, which for gameplay means simplicity and control. Nothing in the game happens without you.

• There are no timers or time constraints of any kind
• There is no randomness of any kind
• There are no real-time elements of any kind. Reaction time is completely irrelevant and you can always take as much time as you want between button presses
• You only ever have to push one button at a time. Buttons are big, do simple and consistent actions and can comfortably be reached with one hand
• You can hold down a button to repeat the action with a delay, for example holding down an arrow button will periodically move you one tile in that direction
• You can undo every action all the way back to the start of the level, with no restrictions whatsoever. There is no punishment for mistakes
• There are no currencies or microtransactions or any other requirements
• You never gain any new abilities or controls. You just move the hook and reel it in, from the first level to the last. Additional mechanics are introduced through the sea creatures and how they interact with the other elements of the level
• Mechanics are consistent. The way each type of creature behaves is the same from the first level to the last
• The whole level is visible at all times. This means you can plan ahead and you don’t need to remember a complex layout
• Almost every level is unlocked from the beginning of the game. This means if you get stuck you can just try a different one and come back later. (See the Progression section below)

Movement Mechanics

You start each level with enough fishing line on your spool to make 30 moves before needing to reel in. At the top of the level is a counter for how many Fish, Crab, Squid and Patrols you still need to catch to complete the level. You catch creatures by moving the hook over them then reeling them all the way in. You can’t cross your own line.

There are four directional buttons (left, right, up, down) and one button to begin automatically reeling in. You can reel in even without a creature hooked. If you’re reeling in with nothing hooked you can push a directional button to stop reeling in and move in that direction. Each individual movement step can be undone. All movement and interactions that occur as a result of reeling in can be undone all at once.

Creature Mechanics

Fish will be killed if you pull them into the stingers of a Jellyfish. Jellyfish and their stingers can’t be caught or moved. Killing a fish leaves behind a Skeleton which you can then pull through stingers to cut them, removing that part of the stingers and all attached parts below. Reeling in a Skeleton doesn’t reduce the Fish counter.

The hook can pass through blocks of Debris but most creatures are too soft to be pulled through. The hard carapace of a Crab can smash the debris, but catching a crab reduces your maximum line length by 5 (pincers and fishing line don’t mix well). Line length is reset to 30 at the start of every level.

Squid leave a trail of 5 Ink blocks behind them. Most creatures can’t be pulled through ink, but Sea Sponges can absorb one block before becoming saturated. Once saturated a sea sponge can’t be pulled through any more ink. Like debris, ink can be used to intentionally drop creatures.

Patrols move when you move, including while reeling in. Each ‘tick’ they will either swim forward one tile or turn around if there’s something in front of them. Like you, they can’t cross your fishing line. They can’t be caught when camouflaged in Seaweed and trying to pull one through seaweed will cause you to drop it. Like regular fish, trying to pull a patrol through jellyfish stingers will kill it and leave behind a skeleton. Skeletons can be used to cut seaweed in a similar way to stingers, removing that part of the seaweed and all attached parts above it.

Undo

There is an unlimited undo. Each press of the undo button will undo all actions that occurred as a result of pressing a different button (i.e. there is a 1:1 relation between the number of gameplay button presses to do something and the number of undo button presses to undo it). For example in the GIF above, after hooking the skeleton the reel-in button is pressed which causes the hook and skeleton to move many places and cut the jellyfish stingers and seaweed; all of these are undone together as they correspond to a single input (reel in).

Putting it all together

Here’s the full solution for one of the later levels which includes many of the mechanics:

The first thing to realise is that the catch counter only has one Fish; it doesn’t matter what else you catch. To get the fish you need to clear the Jellies which means you’ll have to sacrifice the Patrol and use it’s Skeleton to cut the stingers. You can catch it straight away from underneath but then you’ll just drop it in the Seaweed, so you need to clear the Debris out of the way and catch it from above. There’s a Crab in the corner but the fish is in the way… Luckily you can use the Ink that the Squid leaves behind to intentionally drop the fish after moving it, giving access to the crab.

Bosses

Levels 10, 20 and 30 are special Boss puzzles with large unique creatures to catch. There are four boss creatures as the final level has two. These levels are generally about clearing a path big enough for you to catch the boss.

Progression

There are 30 levels in the game and 27 of them are unlocked immediately. The boss levels (10, 20 and 30) require you to complete n-1 levels to unlock them, i.e. you need to complete 9 levels to unlock level 10, 19 for 20 and 29 for 30. Note that these can be any levels, including levels after that boss. For example let’s say you complete levels 1-8 but get stuck on 9, you could then complete level 11 (or any other level) to unlock 10 and face the boss. But you can only unlock the final level by completing all 29 preceding ones. This friendly unlock system solves the frustrating issue of getting stuck in a level-based puzzle game and not being able to progress in any way.

In this example the player has completed 2 levels and needs to complete 7 more to unlock level 10 and see the mystery boss marked as a ? on the minimap:

As well as acting as goals and progression markers, the bosses also serve as rewards in their own right. From the main menu you can access the Aquarium, which shows silhouettes of all the creatures and fills in as you encounter and solve puzzles featuring each one. Since the bosses have much larger and more detailed art than regular creatures they look great as trophies in the aquarium.

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