I keep failing this because Wanikani’s mnemonic is awful: “Slide some dirt on your legs so you can feel like you’re from a previous time” ???
I’ve seen many topics about trouble in memorizing all the different vocabulary that use this kanji but I haven’t seen any about the kanji itself. If you guys would be so kind to share your own mnemonics, I’d be grateful 
Honestly, try to make up your own personal mnemonics, something that you thought of, that formed in your brain. Make it vivid, associate a thought out situation or picture it. This will always help more than mnemonics, someone else made for you, because as you already see, you won’t be able to feel a personal connections with some (or many).
WK gives hints and tries to establish stories that pull you through the whole journey, but that doesn’t mean, they are actually any good. 
Also I’d argue, you only should need mnemonics for a short time, reinforcing them every time you see the item does the wrong thing, it should just build a bridge for a short time until you don’t need it anymore and forget about it anyway, only leaving the link between the actual item and reading.
Even if you find none, even without mnemonics it will tend to stick, so if you have big trouble remembering the item and don’t find a mnemonic, just give it some time, it will stick without. Maybe write the Kanji a few times, thinking about it. Do that a few days for such really hard items and all will be good.
This is a mega common kanji, once you start getting into native stuff you’re gonna see it everywhere so I’d not worry about it too much
Agreed, I tend to create my own micro-mnemonics; they only need to hold up long enough to let the kanji sink in.
I forget what I did for this one, but I like how they tie the reading “sen” to “century” in the hints section. That suggests “previous/past” to me.
I usually do, but I’m somehow not able to create one for this kanji - might have something to do with my brain being shattered from studying to finals 
I’ll try writing as you suggested, thanks ^^
Previous time aside, I can imagine how this mnemonic works.
Perhaps, not to slide, but playground slider, would work better?
So the meaning, see the Kanji in action.
That makes sense, I think I was able to create a good enough mnemonic using this playground slider idea 
I ended up using the WK mnemonic because I couldn’t think of a better one. Fortunately, since the kanji is used in many vocabs like “last week”, “teacher” etc. I got used to it pretty quickly and didn’t need the mnemonic anymore.
For me I connected with the ‘centaur’ mnemonic for the pronunciation, and because I think the character looks like a kind of mythical creature on legs with a bow/weapon(?) in its hand, that worked for the visual component too. Imagining some centaur trotting around in ancient times… hey, YMMV lol
after @polv 's suggestions I came up with “You go down a slide and your legs get dirty. You look PAST: there’s dirt on the slide!!! you look AHEAD and there’s also dirt! your FORMER self was clean, but now there’s dirt past and ahead of you :(”