In Absurdle's challenge mode, you are provided with a target word, and you must force it to be the secret word. It's no longer sufficient to back the game into a corner. You have to back it into a specific corner.
This mode is much more challenging than basic Absurdle. This mode is recommended for advanced players, who have a sound understanding of how the Absurdle AI works.
Here are some key points to remember:
A good basic strategy is to intentionally guess letters which aren't in the target word. Absurdle is very likely to rule them all out, because ⬜⬜⬜⬜⬜ is often the response associated with the largest possible bucket of remaining words.
But this often isn't the case! Here, the target word is "SCRUM". So we guess "PLEAT", which seems like a good guess, because "PLEAT" has no letters in common with "SCRUM". But...
Why did this happen?
Well, if Absurdle's response had been ⬜⬜⬜⬜⬜, that would have left 255 possible remaining secret words. But, with a response of ⬜⬜🟨⬜⬜, that leaves 263 possible remaining secret words. That's a bigger bucket, so Absurdle responds with ⬜⬜🟨⬜⬜.
This in turn means that there is an "E" somewhere in the secret word — which means that "SCRUM" is no longer a possible secret word. We've missed the target! So we have to undo (click or tap "undo last guess", or press Ctrl+Z) and try again.
As the game continues, this becomes more and more problematic. I find that a lot of trial and error is involved. One approach is to slowly eliminate unwanted letters a few at a time, by intentionally guessing words which reuse some letters which have already been eliminated... but this can be slow going and require more guesses than necessary. Later, as the pool of possible letters dwindles, we have to eliminate potential locations of the remaining letters.
Here's a complete sample game by me.
Not shown here are more than a dozen bad guesses which I had to undo.
Anyway, as I say, challenge mode isn't for everybody. If you do decide to tackle it, be assured that challenge mode is always possible — you will never be given a target word which can't be forced. This remains true even when challenge mode is combined with hard mode, but combine modes at your own risk!
Challenge mode has not been cross-tested with expanded vocabulary mode, yet. Again, player beware.
Absurdle ends the game if the target word has been outright eliminated as a possibility... however, there are more complex unwinnable states which it can't detect. If in doubt, undo to the very beginning and start over.
Best of luck!