I like this example youâve given as Iâve made that exact typo.
If youâre on PC I highly recommend the double check script, I wouldnât be using Wanikani without it: [Userscript]: Double-Check (Version 2.x)
Wanikani says the reason they donât have a built in undo button is because they want to prevent users abusing it, but my tinfoil hat conspiracy is that itâs just so that you stay on the same level longer when you make typos so your subscription runs longer
I also advocate for the double check script. I think if you are responsible with it, it will save so much headache.
It happens with me sometimes, it does not bother me that much now a days ,
Its not like you are going to miss type everytime.
even if I miss-type, I simply accept it now a days as part of my fault and move on,
and its not that bad in lower levels.
When you have not GURUd and assume you are just making this kind of mistake, you will just need more time to get it GURUd which gives you more time to spend time with that radical/kanji/vocub which is a big W for me.
I see it positively now a days 
, may sound silly but thinking this way helps you to enjoy Wanikani without any script âŠ
true , I have seen it happening.
something i have learned is if you get the first question of the term wrong go back to your dashboard before it gives you the second question of the term, it wonât level it down.
ex: it gives me âwhatâs the kanji reading for ć·?â and i type âkawanâ (shouldnât have the n) normally a little later in the session, it would ask me âwhatâs the meaning of the kanji ć·?â but i go back to the dashboard instead of finishing the review.
of course, this only works if itâs a kanji/vocab and if youâre on the first question
hope this makes sense, i feel like i explained it badâŠ
CTRL + R (windows pc) will do the same without taking you all the way to the dashboard.
In response to the âclose the windowâ trick, it works even if you have answered both meaning and reading for the item as long as you do not press anything after the mistake was entered and the window turns red. In other words, as long as âguruâ doesnât appear, telling you that the item leveled down. I type really fast and often press enter on autopilot just as I realize I made a typo, so I use this quite often but only when it really was just my butterfingers.
I occasionally do what @Rena56 does, i.e., go back to the dashboard. So heresâ a summary of what happens:
If I did 10 reviews and completed 3 (kanji & vocab), did 3 kanji or vocab only and on the 4th one I make a dumb error, then when I start over again, the 3 kanji & vocab are done and all 4 of the others will reappear.
But what youâre saying with ctrl R is that my review will simply continue, i.e., the 3 items with only kanji or vocab done will show up with the their other instance (vocab or kanji) and the 4th one that I just got wrong will show up for its first instance?
If this is true, then that is a neat trick!!! 
How did you ever discover that? Great job ! Thanks for sharing
I do the same on browser. If I misclicked (or even if I just wasnât paying attention/spaced out and didnât even read the kanji before answering but I know I know it) I refresh and then proceed to get wrong on purpose the ones I actually got wrong when they come up again so Iâm not cheating through those and advancing them when I shouldnât. For me at least, even if itâs the second âhalfâ of the kanji (like if I answered reading correctly but then meaning comes up and I mistype) it will reset it if Iâm still on that kanji and havenât clicked next before refreshing the page.
Iâm surprised to see so many people using the reload the page strategy. Why not just use a script that allows undoing, or if youâre on your phone an app that allows undoing? Then you donât have to remember which previous answers you got wrong and spend time getting them wrong on purpose again. Youâre already trusting yourself not to cheat, might as well give yourself the full power
They could use a warn list for the okurigana. Not sure why they only have one for the English side, and not gor the Japanese one.
Itâs more friction because you lose up to 10 other half-answered items.
@DuoLingo Unfortunately, you do still lose progress on the half done reviews when the page is reloaded. I just find it quicker than going back to the dashboard.
@Fishfulness Why go oit for scripts when we have reload at home?
. Seriously though, I donât bother trying to be honest about the ones I missed before the reload. The "punishment " of having to do all the half done sets again is enough of a deterrant to keep me in line. I am reading Japanese every day and come across words in my review pile that I still wind up looking up. In those cases, I donât purposely fail it during review time. Thatâs just too strict for me. 
I do WaniKani on my phone, and use voice to text for the English.
Ive had this happen to me a ton.
I mean, to me refreshing the page is just simpler. Also, compared to memorizing kanji meanings/readings (which I consider fun rather than difficult) remembering which ones you got wrong is entirely too easy. (And I just donât know how to add a script that allows undoing lol). Even if I did, though, I probably wouldnât need it.
I also think going through the ones you did get wrong an extra time actually ends up helping.
You are a pure oneâŠdo not taint yourself if someone comes forward to teach you the evil waysâŠ
Fair enough, I really just like to speed through reviews and I make so many typos. Thereâs like a 50/50 chance thereâs at least 1 typo with every answer I type, but thankfully thereâs some leeway with accepting some typos. But when I completely mess it up so badly it canât recognize it, thatâs when I gotta break out the backspace to undo. Without it Iâd be refreshing like every 5 reviews. It is very easy to add if you ever wanted to check it out, like 2 minutes. Got a couple other useful features I use often too. [Userscript]: Double-Check (Version 2.x)
I wouldnât mind using a script if it was the occasional typo. But if itâs that many, Iâd rather be forced to slow down and type properly. For me itâs just too tempting to become sloppy otherwise.