Teaching without words

In my new level, Island of Mimir, I put in a challenge that is giving some players a lot of grief. (See attachment.) To pass up between the spikes you get on the wall. You press jump without touching the directional keys. You'll slip right through that narrow gap. It's easy, but only if you know how.

I tried to teach it 2 screens previously by having a similar situation with only one monster. You can surpass that screen without learning what I was trying to show. A written explanation in-game would break the atmosphere. How can I teach this move to players through challenges or simple symbols?

I had a similar issue with 'I Dreamed of the Sky'. In one of the areas in the second half of the game, you have to climb up some pipes which have sticking-out joins. You can pass these in the same way, just by jumping up, but a lot of players commented about how hard they were the climb. It feels like something people are going to struggle to discover naturally, since it's such an unrealistic behaviour.

Regarding Mimir: I actually did pick up on that hint eventually when I got there. At first I was like: "wait, did I just softlock myself by saving here? I'm not softlocked, right?" It took me a few deaths to realize WHY the gap between the two enemies was slightly to the right of the left wall. I completely forgot that Juni did that when jumping off of walls. I guess I don't see levels making use of that mechanic often.

Just pointing out it doesn't have to be an entirely neutral jump. I got through the gap by jumping off the left wall while moving right and holding A.

At first I was like: "wait, did I just softlock myself by saving here? I'm not softlocked, right?"

I do try to be a designer you can trust not to intentionally soft-lock you. I also try to avoid anything too complex or pixel-perfect. I even try to avoid jumps you can't make but look like you might if you did it just right. This challenge has shown itself to be more obtuse than I thought it was, so it doesn't fit with my design philosophy. I still like it, so I want to figure out a better way to present it rather than change it.

Since I might have been the first one, who struggled with this section, I post my thoughts about this again, even if I have already done it on Niffcord.
Seeing that part, I was a bit confused, how that challenge be beaten. After a few silly attempts trying to jump over both of the enemies at once, I finally convinced myself to trust the level designer the savepoint is intended. Knowing you, it was not much hard, but maybe playing it without this context, it might have stopped me there. Fortunately that was not a case and after some time I managed to jump out the gap. After playing, I just wanted to share my achievement I managed to get out, together with my initial thoughts so the posted this image with a title "This is a nice place to stay". Thanks for learning a new mechanic, I did not know about (intentionally)

I put together a little experiment. I'm using death-warps to insert a hint after you die three times. You have to save between the monsters to activate it. The spikers are a little glitchy here, but I could replace them with tiles on the spawning screens. Let me know what you think.
egomassive.com/nifflas/mimir.knytt.bin

I think you did a good job originally. For what you wanted to communicate without explicitly telling the player what to do, a frictionless experience is probably impossible. This hint message is a neat trick, but I prefer nothing.

I had a reaction similar to SC. At first glance I thought going down there might softlock me. So I intentionally saved there after a second attempt at the gap. Then I realised since I could get in, I could get out. So it took me a few tries but I got out and over and realised it was probably the intended solution.

I've had to make tutorial sections in a few of my Portal 2 levels, so I know the problem.

What you want to do is force an easy challenge onto a user where it is obvious that it is a challenge that one can overcome. Put it right before the harder challenge and they'll get it.

In order to do the first, make sure the player goes to a one-way area with save point and a warp. The user saves first, then goes into the warp. The warp brings them to the training room where they have to perform the task. If they die, they get back to the earlier place without any option to go back. They'll learn the challenge is beatable, and then find a way how to. Then they've mastered the technique, and it can be used in your actual challenge.

The important part is to create an area with savespot that cannot be escaped and will not question the player whether they should save or not.

Wow, thanks for all the feedback everyone! I think the problem with teaching this move is there is no easy version of it. Even in this case where you have to figure it out or stay stuck, canteven found a different solution. I discovered the move playing Color Coordination by Little Pineapple (Purple Pineapple's little sister) in case anyone's interested. She put death blocks in the walls which can just barely be jumped past.

Although I didn't intend for it to be such a stumbling block, it seems people are still enjoying the challenge and figuring it out. I guess the best thing to do is leave it alone. I'll put a hint in the level's opening post, for those who get truly stuck.

@LPChip: I like the method you've described. Points of no return are an important tool. Too many times I've looked at a challenge and thought, "I probably need the umbrella for this." Then I go on a fruitless backtrack through the whole level when I didn't need the umbrella. If the designer had trapped me there, then it would have saved me a lot of trouble.