I currently am unable to play Club Penguin Island but thanks to the Discord server, I can view the challenges. As such, here’s a guide on how to complete them with very little pictures. Sorry!
Firstly, as a member, you’ll need to have a shark costume. You might have this from a previous challenge and if you do, simply wear it. If not, tap the blue button at the bottom of your screen, go to “My Designer” and buy a shark costume. Decals and fabrics don’t matter! Next just put it on.
Gather 4 friends who are also wearing the “Sea Shark” costume and head over to the Party Submarine. This can be done by travelling a bit deep in the Sea Caves and sticking to the left. Once you’re all there, you can claim your reward.
Park It at the Market:
Dive into the Sea Caves and swim to the veryyyy bottom. You’ll go past the Throne Room and the Crab’s Den where you’ll eventually get to the Grow Grotto. Head over to the Party Supplies market like in the image below and tap the orange interactive button to claim your reward!
Head over to the Party Submarine in the Sea Caves and swim over to the left lever and tap it using the orange interactive button. Then swim around the Party Submarine to claim your reward.
Swim opposite the Crab’s Den entrance and past the entrances to get to the Throne Room in the Sea Caves.
Sorry this guide is so short, not much I can do at the moment despite the significant events that are happening at the moment.