RAT RUN 21: Friendly
(Published on 14. January 2026, 01:00 by marty_sears)
- Normal sudoku rules apply.
- AIM OF EXPERIMENT: Finkz and Phinx must both reach the cupcakes by finding a path through the maze. The paths must not visit any cell more than once, cross themselves or each other, or pass through any thick maze walls. The paths may not share cells except for where they meet at the cupcake cell.
- As well as moving orthogonally, Finkz and Phinx may move diagonally if there's a 2x2 space in which to do so, but may never pass diagonally through a round wall-spot on the corner of a cell.
- BLACKCURRANTS: If two digits are joined by a blackcurrant, one is double the other.
- GRAPES: If two digits are joined by a grape, they have a difference of at least 5.
- FORBIDDEN DOORS: If two digits are joined by a red X, they sum to 10. Finkz and Phinx may not pass directly through a red X.
- TEST CONSTRAINT: In this experiment, a cell may only be visited by Finkz or Phinx if its digit matches its row number, column number or box number. (Boxes are numbered 1-9 in normal reading order from top left to bottom right.)
Solution code: Digits in row 3 NOT visited by either rat, from left to right
Comments
on 5. February 2026, 02:10 by ongel
I'm so glad I stuck with this and it was so rewarding making it through! my first successful rat run but definitely won't be the last :)
on 27. January 2026, 01:37 by EMCaoloft
A thing of beauty <3
on 20. January 2026, 07:42 by rhyrhy
80 minutes, even with some hints. I should try once again without any hints. Always thanks for beautiful puzzles!
on 19. January 2026, 17:15 by extremelypuzzled
We are so back, thank you!
on 18. January 2026, 19:00 by BG03
Only Marty's sense of humour can make Finkz and Phinx so ridiculously evenly matched!
Thanks for working season 3 - this series is the undisputed crown jewel of LMD!
on 17. January 2026, 01:37 by ChristopherStanlake
Oh we are so back!
on 17. January 2026, 00:43 by MikeMeech
Welcome to the party Phinx!
on 16. January 2026, 22:59 by goldpuffle
So... which rat is which?
on 16. January 2026, 21:07 by wuc
Brilliant start. 3.5* to me. Hungry for more thx.
on 16. January 2026, 19:09 by Klausku
Beautiful and brilliant. Perfect start of season 3. Can‘t wait until copyrat comes out. Thanks Marty!
on 16. January 2026, 18:32 by eladv
This was so much fun!! The first set of deductions (which I wasn't spoiler here, but I will write in the hidden comments) was one of the most beautiful I've ever seen. And we even got a more-intricate version of it deeper into the puzzle! This test constraint was a perfect match to the two-rats puzzle. I'm so stoked for the season, this is going to be grand!
on 16. January 2026, 17:08 by ufdigga
I'm so happy to see Finkz is back!
on 15. January 2026, 23:41 by VolpeRosso
So excited that these are back - just what is needed to distract from 2026 <3 Some wonderful logic, especially a step in the middle when I was *certain* it was impossible until I saw the "one little trick". Thanks so much, Marty! <3
(Edit: I am, however, slightly apprehensive about the phrase "this concluding phase" in the Experiment text... However, all good things must come to an end, and I'm sure Marty will come up with something equally delightful for his next long form project!)
on 15. January 2026, 16:58 by olc
my first rat run! very satisfying but had to restart twice because i messed up the logic along the way...
on 15. January 2026, 12:07 by mscha
Finkz is back! And Phinx! Yay!
Very tough start of series 3, definitely 5 stars for me. But (as always) very nice!
on 15. January 2026, 11:20 by davidz32z
Love love love! Took me awhile to get back in the mindset, can't wait for the rest of the phase <3
on 15. January 2026, 05:21 by etoler
I'm really trying hard not to cry about the lonely Sudoku rat who finally met a long-awaited friend. Unfortunately, I'm a sucker, so it's a battle I'm destined to lose.
on 15. January 2026, 01:46 by Atticus837
A beautiful way to return to the series, and a lovely introduction for Phinx!
Can't wait for the next one.
on 15. January 2026, 00:21 by Ratfinkz
Loved it!!! So worth the wait :)
Glad I solved by myself too and ignored those people haha
Also... that picture at the bottom is adorable!
on 14. January 2026, 23:59 by Flinty
Very nice! :)
on 14. January 2026, 21:08 by blackjackfitz
Huzzah!
on 14. January 2026, 20:11 by Calvinball
Triumphant return to the series. Also mad respect to marty because at some point he's going to have to update the graphics on over 60 lmd puzzle pages for this lol.
Marty: haha that is starting to take longer than actually designing the puzzles
on 14. January 2026, 19:55 by dzamie
Woo, new rat run! Good to see Finkz is doing well, and remains friendly with her new friend.
on 14. January 2026, 19:20 by bboom
Lovely to have a new set of rat runs, and this one held up the tradition of looking fairly impossible at the start, and still solving in a very reasonable time anyway.
Also Phinx is clearly the cuter looking one!
on 14. January 2026, 18:45 by vfig
twice as many rats, twice as hard to get started (or so it seemed to my sleepy brain). not my favourite constraint type but an excellent choice thematically. super excited for the continuation of the series!
on 14. January 2026, 18:41 by CorpJigsQuand
Harder than expected. Then realized that the non-black dots are green and nothing has to be consecutive...i would be a terrible rat.
on 14. January 2026, 15:56 by nunc
Hard, but beautiful. Thanks a lot. I'm looking forward to the next puzzles!
on 14. January 2026, 14:48 by Exigus
Delightful. Thanks!
on 14. January 2026, 14:31 by Franjo
Welcome back, Finkz and Phinx! I’m so happy to meet you again. Thank you very much, Marty, for creating and sharing another episode of the most popular puzzle-series the world has ever seen.
on 14. January 2026, 14:19 by Myfyr MJ
That was great fun. Can’t wait to see what Simon makes of this one.
on 14. January 2026, 14:08 by QuintusScaevola
These puzzles are just an absolute delight. Thank you Marty.
on 14. January 2026, 13:58 by Tortugo
I am just getting started, and I’m not sure if the paths are allowed to be “tangent” to one another. For example, can path 1 enter a cell from the left and exit up, while path 2 enters the same cell from the right and exits down? I think the rules as stated do technically prohibit this but one could argue they don’t.
Anyway I am so glad Finkz et al. are back and I can’t wait to struggle through this season.
Marty: thanks for the feedback, I have tweaked the wording of the rules very slightly which should hopefully clarify things
Tortugo: thanks for the rule clarification, and so sorry for the spam… I wasn’t refreshing the page intentionally, so I assume it has something to do with the way my phone’s browser loads up all my open tabs every time I reopen the app.
Oh and the puzzle was as beautiful and fun as ever.
on 14. January 2026, 12:07 by raaaaa
Great puzzle! But I found a little bug, did you forget to change the link about 21 in the previous puzzle? I tried to return to this puzzle through other previous puzzles but failed.
Marty: Yes I haven't gone back yet and updated all the links in previous puzzles. The bigger the series gets, the longer that takes!
on 14. January 2026, 10:40 by alexsmart
> So, who is who?
Maybe the big reveal at the end of this series would be that the rats are, in fact, indistinguishable quantum particles like photons (excitations of the same underlying RAT field perhaps) so the question would be meaningless.
on 14. January 2026, 06:59 by vfig
cannot wait to solve this one tomorrow morning!
on 14. January 2026, 05:56 by Angara
So, who is who? Thanks for this brilliant!
on 14. January 2026, 03:42 by KelleyCook
I'm on team Phinx!
on 14. January 2026, 02:35 by chinesemaster
So brilliant! Thanks so much for bringing Finkz back!
on 14. January 2026, 01:18 by sujoyku
Yay, Rat Run is back! Thank you for the new season, Marty! You start it off in style: with another banger of a puzzle.
