Fortnightly Topic Challenges are all water under the bridge now, so we will do something completely different.

What to Do:

If you have an idea for a tag or a theme of any kind to use as a topic challenge, post it as an answer below. (Do note, you can propose anything, not only a tag). Each answer should start with the title of the topic in a markdown heading (## Title ##). Only one suggestion per answer, please. Here is a list of all tags, to help.

At the start of each month, the highest-voted answer to this post will be selected as that month's topic. Starting from today, users can propose their themes or topics. The selected answer will then be deleted to reduce clutter in the list.

After the selection, a new question will automatically be created in this format. An answer will then be posted to that question with links to all the posts in the featured topic in the fortnight.

We'll again keep a list of all the topics.

Happy Puzzling!

The first MTC will start on July 1st, 2022. In the meanwhile, topics will be gathered and voted on.

  • 2
    $\begingroup$ Is this event going ahead? (Asking for a friend...) $\endgroup$
    – Stiv
    Jan 3 at 23:14
  • $\begingroup$ @Stiv Sorry all, wasn't able to be active here for 6 months. Sure, we could start in July if it's still relevant. Or perhaps a return of the chain puzzles? $\endgroup$ Jun 15 at 18:44
  • $\begingroup$ Publicise it in TSL and I'm sure people would start contributing once others do. I think July works well for a starting time :) $\endgroup$
    – Stiv
    Jun 15 at 19:09
  • $\begingroup$ How is this different from Fortnightly Topic Challenges? $\endgroup$
    – melfnt
    Jul 9 at 7:13
  • 3
    $\begingroup$ @melfnt In no way other than its length. $\endgroup$ Jul 9 at 7:15
  • $\begingroup$ @LukasRotter ok then, can I copy here some of the topics proposed for the last FTC that were not used due to the lack of activity? $\endgroup$
    – melfnt
    Jul 9 at 8:50
  • $\begingroup$ @melfnt Sure, go ahead :) $\endgroup$ Jul 9 at 8:52

9 Answers 9


Restricted Title: xkcd 1xxx

See this FTC, which dealt with the first 1000 xkcd comics

Usually the title is decided upon later in the puzzle creation process, chosen to be fitting and often to provide a hint/reference. Here we're going to go the other way.

Below is a list of the titles for xkcd comics 1000-1999, filtered down to those titles which are a valid Stack Exchange question title (≥ 15 characters). Pick any of the 300 remaining titles and use it as-is (preserving case, part numbers, parenthesised words, etc.) — this will be the title of your new puzzle.

The title should make sense given the puzzle, whether that be through the puzzle's presentation, mechanics or answer. The more fitting, the better!

Don't be discouraged if you see that someone else has posted a puzzle with a title you had intended to use. If anything, it can be interesting to see what different approaches people take for the same title, should there be any collisions!

The list:

Sloppier Than Fiction
Wrong Superhero
Wake Up Sheeple
Valentine Dilemma
Backward in Time
Good Cop, Dadaist Cop
So It Has Come To This
Compare and Contrast
Lakes and Oceans
Whites of Their Eyes
Every Major's Terrible
Words for Small Sets
Home Organization
Argument Victory
Eyelash Wish Log
Internal Monologue
Formal Languages
Clinically Studied Ingredient
A Hypochondriac's Nightmare
Sports Cheat Sheet
Cautionary Ghost
Think Logically
Killed in Action
Blurring the Line
Electoral Precedent
The Universal Label
Objects In Mirror
Epsilon and Zeta
Frequentists vs. Bayesians
Rubber and Glue
Calendar of Meaningful Dates
Nothing to Offer
Kolmogorov Directions
Drop Those Pounds
Star Trek into Darkness
Moving Sidewalks
Those Not Present
Virus Venn Diagram
Rembrandt Photo
Circumference Formula
Ineffective Sorts
Stratigraphic Record
All Adobe Updates
Integration by Parts
Is It Worth the Time?
Footnote Labyrinths
Birds and Dinosaurs
Interstellar Memes
Combination Vision Test
Sticks and Stones
Balloon Internet
The Pace of Modern Life
Realistic Criteria
Douglas Engelbart (1925-2013)
Quantum Mechanics
Annoying Ringtone Champion
10-Day Forecast
The Mother of All Suspicious Files
Exoplanet Names
Preferred Chat System
Halting Problem
Alternate Universe
Privacy Opinions
Tall Infographics
Reverse Identity Theft
Improved Keyboard
Syllable Planning
Shoot for the Moon
Telescope Names
Exoplanet Neighborhood
I Don't Own a TV
File Extensions
Undocumented Feature
Buzzfeed Christmas
Christmas Lights
Infinite Scrolling
Goldbach Conjectures
Questions for God
Mobile Marketing
When You Assume
Types of Editors
Before the Internet
Shouldn't Be Hard
Cosmologist on a Tire Swing
Heartbleed Explanation
Airplane Message
Orbital Mechanics
Google Announcement
Astronaut Vandalism
Manual for Civilization
People are Stupid
Clumsy Foreshadowing
Subduction License
Research Ethics
Dominant Players
Quantum Vacuum Virtual Plasma
Universal Converter Box
Worst Hurricane
March of the Penguins
Teenage Mutant Ninja Turtles
Suddenly Popular
My Phone is Dying
Reduce Your Payments
Move Fast and Break Things
The Sake of Argument
Where Do Birds Go
Presidential Alert
AI-Box Experiment
Background Screens
Trolley Problem
Location Sharing
Apollo Speeches
Fundamental Forces
Stories of the Past and Future
Terry Pratchett
Upside-Down Map
Ontological Argument
Operating Systems
Scenery Cheat Sheet
Basketball Earth
Win by Induction
Typical Morning Routine
Sword in the Stone
Placebo Blocker
Antique Factory
Scheduling Conflict
Strengths and Weaknesses
Tamagotchi Hive
Solar System Questions
Exoplanet Names 2
Water Phase Diagram
Every Seven Seconds
Synonym Movies 2
Engineer Syllogism
Car Model Names
Trouble for Science
I Could Care Less
Picture a Grassy Field
NASA Press Conference
Moments of Inspiration
Keyboard Problems
Hardware Reductionism
30 Days Hath September
Launch Status Check
Linguistics Club
Five-Day Forecast
Food Combinations
Baking Soda and Vinegar
The Three Laws of Robotics
Watson Medical Algorithm
Christmas Settings
2016 Conversation Guide
Substitutions 2
Longer Than Usual
Possible Undiscovered Planets
In Case of Emergency
Super Bowl Context
Gravitational Waves
United States Map
Universal Install Script
Estimating Time
Captain Speaking
City Talk Pages
Laws of Physics
Arcane Bullshit
Timeline of Bicycle Design
Message in a Bottle
Full-Width Justification
Recent Searches
Substitutions 3
My Friend Catherine
Time-Tracking Software
Phishing License
Intervocalic Fortition
Theft Quadrants
Speed and Danger
Home Itch Remedies
Genetic Testing
Walking Into Things
Time Travel Thesis
Meteorite Identification
Linear Regression
Number of Computers
Migrating Geese
Earth Temperature Timeline
Fashion Police and Grammar Police
Manhattan Project
Datacenter Scale
Fixing Problems
Spider Paleontology
Future Archaeology
Interplanetary Experience
Tornado Safety Tips
Never Seen Star Wars
Startup Opportunity
Adjective Foods
Things You Learn
Interest Timescales
Appliance Repair
Bad Map Projection: Liquid Resize
Telescopes: Refractor vs Reflector
Soda Sugar Comparisons
All You Can Eat
Bad Map Projection: Time Zones
Decision Paralysis
Location Reviews
Unpublished Discoveries
Borrow Your Laptop
Best-Tasting Colors
Rayleigh Scattering
Security Advice
Existential Bug Reports
Hottest Editors
Identification Chart
Survivorship Bias
ISS Solar Transit
ISS Solar Transit 2
Photo Library Management
Random Obsessions
Machine Learning
Genetic Testing Results
Anti-Drone Eagles
Glacial Erratic
Air Force Museum
Existence Proof
Sports Knowledge
Particle Properties
Wifi vs Cellular
Russell's Teapot
Physics Confession
Eclipse Flights
Positive and Negative Reviews
Emoji Movie Reviews
Backup Batteries
Geologic Faults
Computers vs Humans
Eclipse Searches
Eclipse Science
Earth Orbital Diagram
Supervillain Plan
Ringer Volume/Media Volume
Typing Notifications
Two Down, One to Go
Obsolete Technology
Worrying Scientist Interviews
Active Ingredients Only
Making Progress
Credit Card Rewards
Digital Resource Lifespan
Defensive Profile
Twitter Verification
Nightmare Email Feature
Temperature Preferences
How to Make Friends
Interstellar Asteroid
The Moon and the Great Wall
Self-Driving Car Milestones
Argument Timing
Virtual Assistant
The True Meaning of Christmas
IATA Airport Abbreviations
Meltdown and Spectre
2016 Election Map
The Food Size Cycle
Memorable Quotes
Universal Dreams
The End of the Rainbow
Scientific Paper Graph Quality
Campaign Fundraising Emails
Chicken Pox and Name Statistics
Super Bowl Watch Party
Backpack Decisions
The History of Unicode
Impostor Syndrome
Self-Driving Issues
Namespace Land Rush
Spatial Orientation
Background Apps
Smart Home Security
Conversational Dynamics
Friendly Questions
Congressional Testimony
Turkish Delight
Rickrolling Anniversary
Python Environment
Research Areas by Size and Countedness
Fatal Crash Rate
Business Update
Selection Effect
  • 1
    $\begingroup$ Is this on for January? $\endgroup$
    – Amoz
    Jan 1 at 15:09
  • $\begingroup$ @Amoz If this isn't confirmed I might go ahead and post something off this list this month anyway. It may even be worth extending the first 'MTC' to cover Jan and Feb, as it seems we may need a little more publicity for this to be more widely known about and participated in. $\endgroup$
    – Stiv
    Jan 6 at 8:30
  • $\begingroup$ @Stiv Cool, I also already posted something off the list this month. Best publicity might be to simply start? Do we know where LR is? Or I can assist if needed. $\endgroup$
    – Amoz
    Jan 8 at 3:01
  • 1
    $\begingroup$ @Amoz We'd probably need a separate meta post for the month's challenge, in the same vein as previous Fortnightly Topic Challenges. 9 days in to the month now, it would be good if it could be started sooner rather than later. Is 7 upvotes sufficient interest to go? Will post in the chatroom too to gauge interest from regulars. $\endgroup$
    – Stiv
    Jan 9 at 15:01

IQ Puzzle Parody

With frustrating regularity, PSE goes through periods of being overrun by requests for help with IQ questions found online or in interviews - most commonly of the type "Here's a bunch of boxes containing some kind of pattern - what image should go in the last box?" Often these questions are low-effort contributions to the site and highlight the very worst of 'guess what I'm thinking' type corporate exercises...

This is ripe for parody!

I propose a challenge where the user should strive to create a puzzle that resembles one of these IQ puzzles but actually disguises another puzzle or puzzle mechanism altogether. The multiple-box design could, for example, lend itself nicely to puzzles, s or puzzles with another clever component.

There's a world of possibilities here, and the opportunity for some fun at the expense of a widely disliked puzzle type...!


Throwing a purely tag-based one in...

Games meant to be played with a pencil and paper tend to be simple little time wasters. But that doesn't mean they can't be incorporated into puzzles in interesting ways! Their very simplicity means puzzles with them can still be easily understandable/accessible even if a little more complex.

This challenge is to create a puzzle deserving of the tag, or a related one like , even if using it would be a "spoiler" - so a which is edited into the list of challenge puzzles after a solve is perfectly fine. Puzzles would be about the pencil/paper games (strategy etc.), simply incorporate ideas/rules from them in some way (e.g. a Sudoku which has a Dots and Boxes variety rule), or involve such a game in some other significant part of the solve process.



The challenge here is to produce a crossword wherein some (or all) squares are filled not with typical English alphabet characters, but with something else altogether.

Such a crossword might contain no English alphabet characters at all (e.g. each square instead contains an image, a special character, a number, etc.) or each answer within it features at least one square containing one such alternative... Crucially, no words in the grid should appear fully spelled out with English alphabet characters.

Note: This is not merely a repeat of FTC #43: Variety Crossword Grids from November 2020 - here it is the content of the squares wherein the variety lies, as opposed to the structure of the grid...



Create a puzzle where the first step is a whose solution reveals further steps that must be taken. Crucially, the full puzzle is entirely self-contained within the nonogram and flavour text. (i.e. Not just using a nonogram as the first step in a long string of grid-deduction puzzles which require additional grids to be displayed in the post.)

Good examples from the past include these two puzzles by @jafe, one of which conceals a and the other a set of puzzles.


copied from Fortnightly Topic Challenges Threrun: Topic Suggestions originally posted by Lukas Rotter

Cellular Automata

Here's a regular tag that doesn't seem to get much love:

This can involve puzzles about a well-known cellular automaton, like for example Conway's Game of Life, or a cellular automaton you've created on your own!

Get creative! Maybe we need to reverse-engineer something, try to produce a certain output with given starting conditions, or something entirely different! Crossovers are of course allowed and encouraged.

Great examples of puzzles on this site are Game of Life: Kill the Sun, Can you recreate this fractal I randomly made? and Checkerboard Infection


copied from Fortnightly Topic Challenges Threrun: Topic Suggestions originally posted by Bubbler

Möbius Strips, Klein Bottles, and other unusual topological surfaces

enter image description here

Imagine an elastic square as above. If you ignore the red edges and glue the blue edges so that they have the same orientation, you get a Möbius Strip. If you join both pairs of edges, you get a Klein Bottle. This is not the only interesting surface; you can have 12 different topologies in total by joining two pairs of edges of a square, which include:

enter image description here enter image description here enter image description here

(The last one is a plain torus.) The universal rule is that, if you're on the surface and you walk through an edge, you enter back to the grid through the matching edge with same orientation.

For example, consider this 4x4 grid:

A1 A2 A3 A4
B1 B2 B3 B4
C1 C2 C3 C4
D1 D2 D3 D4

Assume the Klein bottle topology at the top. If you're at B1 and walk left, you end up at B4 (by going through the red parallel edge). If you're at A2 and walk upwards, you end up at D3 (by going through the blue twisted edge).

For the first one on the second image set (the one where the matching edges are adjacent to each other), if you walk upwards from A1, you enter back at A1 but facing right!

The challenge is to create a puzzle that involves an unusual topological surface (which excludes plain wrap-around mechanic a.k.a. cylinder and torus). Such a puzzle may involve tiling, graph, crossword, or a grid-deduction genre, among others.

Some good examples:

You can search for puzzles containing torus, toroidal, or wrap around for some ideas.

There is even a programming language called Klein that can run the same code on different topologies!


Is it really that again?

After the first monthly challenge, I expressed my sadness for not seeing Randall Munroe's best work, the 1190th comic, Time. And then I noticed Puzzling had a tag with the same label as that missing comic!

So, I propose a challenge to create puzzles revolving around time, be it near or far, referencing the "unstoppable progress of existence", or even just the comic. A puzzle that comes to mind when I say this could be this one, but there are many more examples, and even more possibilities!

Because after all, why do people solve puzzles if not to have a good time?


mobile-friendly puzzles

Why is this post so badly formatted you may ask? Well it's because I am dictating into a mobile phone.

a lot of us are busy and on the go these days and don't have time to sit at the computer and solve puzzles but we'd still love to have some fun. I propose for the monthly topic challenge mobile friendly puzzles. These are puzzles which can easily be solved on your mobile phone using common knowledge or perhaps looking up a few things, but not poring over complicated charts or graphs, using Excel, filling out drawings, or requiring extensive markup or time writing out a beautifully formatted entry.
Creating a good mobile-friendly puzzle is a true challenge for a Puzzle Master for they must create a puzzle that is simple enough to be viewed and solved on a mobile device and yet elegant, interesting, and unique. It should be answerable in a few lines of text or perhaps by uploading a simple screenshot with minimal markup.
There are plenty of examples on this site; here's one at random: It's a... Ohh... puzzle (BpFp)

In the spirit of this being a Challenge, entries should be innovative and new in some way, to the op's knowledge. For example:
-Something that looks like an affix-riddle or What is a Word, but is actually something else entirely, or takes a new or unexpected twist.
-A puzzle with a visual component leveraging a never seen before mechanism.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .