I know someone else recommended it earlier but the doublecheck userscript is awesome, has made me enjoy Wanikani a lot more.
When I get a wrong answer, I’ll judge if it’s really something I need tested again if I get it wrong. If it’s a radical with a name that’s only loosely connected to any kanji…I’m a lot more loosey-goosey with it and will click retry it if I’m “close enough”. Like, do I really need to know “Triceratops”? Not in the grand scheme of things and hey, I ended up learning it anyway!
Is it a word that I definitely knew as soon as I hit send, and just brain-farted on? I might retry it anyway because, hey, I just reviewed it there and I KNEW the reading, that counts for something.
But if it’s an important word, one I feel I’ll mess up later, then I’m a bit harder judging whether to retry or not.
For ones I slip up on often I will pause to try and read the description again, try to find a specific mnemonic for it, etc. Maybe try even making flashcards of just the leeches somewhere. Try writing sentences with them, or look at the example sentences, to put them into context.