Though this one will be a little tricky and time consuming, the outcome will be an awesome Leviathan skin costume -- which will totally be worth it.
The key components to this one will be a breathable clear helmet ($18.90) and a fish mask ($6.00). But before you put on the clear helmet, make sure it's safe and breathable.
To recreate the fish himself, you can either get creative with green and pink face paint as well as color hairspray or you can purchase cheap printable fish masks from Etsy.
The main hiccup you might run into is with the suit. Despite there being few suits available that are identical to Leviathan’s, you can pull it off with a grey/white onesie or jumpsuit and tan gloves from Amazon.
Here's what you need for this Fortnite costume: