Slip wall is the above image. You have to climb to the top by rope. And then, you have to get off the ladder. You might need your arm strength. But I think this is easier compare to the other obstacles.
Difficulty level I think: ★☆☆☆☆
I used the following shoes at the spartan race in Aizu. My shoes don’t have grooves, in other words, very flat. But I didn’t slip at all on the slope.
Many people stop in front of this obstacle once. But I recommend you don’t stop, I recommend you run through this.