This is a third-party script/app and is not created by the WaniKani team. By using this, you understand that it can stop working at any time or be discontinued indefinitely.
https://greasyfork.org/scripts/233-wanikani-levelup-celebrator
This is for those of you who would enjoy a little more fanfare when you go up a level! It’s an accomplishment, and it should be celebrated!
This script will display an image and a text message on your WaniKani dashboard when you level up. You can customize both the image and the text.
A picture is worth a thousand words, so please take a look at the screenshots below.
This is the built-in screen:
(That’s an animated GIF with gently falling sakura.)
Customizations are available via the GreaseMonkey menu:
Here’s the Set Image URL dialog:
And here’s the one for changing the text:
If you want to do any fancy text formatting, you need to use HTML codes (<– link). For example, the <br/> you see there is how you do a newline. You can also do bold, italic, etc. Click the link for more info.
Here’s the result of those two customizations:
And here’s another option:
After you level up, the display will be shown the next time you visit the dashboard, and will remain enabled for the following 10 minutes. After that, the party’s over, and you need to get back to work. 
Anyway… I hope you enjoy it!
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Version 1.1
I added a Preview command to the menu, so you can see what the display will look like. This is helpful when you’re trying to customize the display.
Choosing the Preview command will bring up this dialog:
To see the preview, click OK and then wait for the page to refresh.
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Version 1.2
You can now put the level number into your text by using the keyword #LEVELNUM#For example:
When your text is displayed, each occurrence of #LEVELNUM# will be replaced by the current level number:
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Version 2.0
This version will also notify you of other notable achievements, like “First Burned turtle”, “2000th Master turtle”, etc.I also reduced the text size by 25%, which seems to work a little better. And, the Preview command goes right to the display, instead of going through a confirmation dialog.
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Version 2.2
Updated to work with the new changes to the WaniKani website as of May 22, 2019.----------------------------------------