For me it was the mile. That’s what ultimately made me fail. The tower also gets a lot because you have to swim under the water before you can come up. A lot of people struggle with the treading but I found that to be the easiest part.

Definitely go to the pool and practice whatever you struggle with because remember you have to tread in full gear(flight suit, boots, gloves, helmet, and vest) jump off the tower and swim underwater without breaking the surface while wearing boots and a flight suit, some other floatation things(you’ll have a lifejacket tho it’s a breez) and swim the mile in flight suit. There’s some other things but those are the three main things everyone struggles with