Subtypes

Aquaghouls can also simply be made of waterproof fabric as well. To swim in the water, most of them have easy to access slits in unnoticeable places to put weight in.
For emergency fixes, these ghouls usually carry around some kind of sealant. Then, heat can be used to seal the plastic back together, creating a type of scar.
These ghouls also commonly have webbed paws or hands to propel them through the water.

You need an Aquaghoul MYO Token to create this type of ghoul.

Any type of closed, airtight helmet, swimming head accessories, or gills
Helmets can be made of glass, plastic, or any other hard material.
Goggles, aquabreathers and other types of accessories are allowed.
Gills are a popular choice for ghouls with an Aquatic body species.
Hoods are allowed, it's just uncommon amongst ghouls. 

Any type of closure that has a seal
Water valves, plugs, tape, sealed holes (glue, caulk, etc) are all parts of aquaghouls. There can be no zippers, no velcro. Anything that will eventually let water in is not allowed. To keep the ghoul safe, it must be airtight and not allow water inside. Liquids spell danger for ghouls since liquids have denser molecules than air does.

Buoyant/weighted fillings
Fillings are usually air and some kind of weight. If using a filling that isn't air, it must be fully contained inside of the ghoul. If a ghoul gets waterlogged, it could mean trouble since they will be trapped at the bottom of a body of water.

Tags
Tags are very tricky to attach to an aquaghoul, since nothing can puncture the ghoul's body. Due to this, bracelets with tag charms are allowed along with necklaces. Sometimes tags can be sown inside of the plastic and sealed, but it is a difficult task and pulling on/ripping the tag increases the risk of a ghoul getting waterlogged.