Below are types of Tidal Class dragons stated in the movie, the show and the video game. If I missed any, don't hesitate to PM me.
Common dragons are allowed by any members, while the rare can differ between Mods and Admins
Legend:
T=Trainable
UT=Untrainable
UK=Unknown
Level 1=Very Common
Level 2=Common
Level 3=Uncommon 100 posts and up (Also, mods and up)
Level 4=Very uncommon-350 posts and up (Also, mods and up)
Level 5=Rare-400 posts and up-Must get permission from an admin or mod (Also, admins and up)
UR=Ultra Rare-Only admins are allowed to make these, and even then they must have at least 500 posts, the dragon can only be used for site events
Tidal Class 
A class of dragons that live under underwater. A Scauldron is used as a symbol of the Tidal Class.
Scauldron T Level 3
The Scauldron is a type of dragon that lives underwater. They are extremely effective swimmers.
Instead of breathing fire, Scauldrons have the ability to scald their victims. This ability comes from sucking in seawater and then heating it in their cauldron-like stomachs before they scald its next victim. This is how they got their name. Scald + cauldron= scauldron. One hit from that hot water will finish off most enemies. They are, like most of the dragons, classified as "extremely dangerous" in the Dragon Manual.
If you want to train a Scauldron, the best way to start is simply to cover yourself in water. Scauldrons are sentimental creatures who love anything that reminds them of home.
This dragon is gigantic. It is a huge sea lizard that walks on four stubby and powerful legs. They have intense obesity to heat the water they suck in. It's tail is like a fish, helping it to swim. When filled with water, the Scauldron's stomach protrudes out and becomes very round. Its neck is very long and thin, and its head is usually fairly slender with its bottom jaw having a sort of pouch that hands from its chin.
Its bottom jaw is very flexible, and it bulges out when filled with water. Its eyes are located near the front of its face, and it has a thin, curving nasal horn. It has peg like teeth that are ideal for catching fish, very sharp, and also happen to be venomous. Two string-like whiskers are connected to the Scauldrons' upper jaw. They have only been seen in three colors: turquoise, green, and pale blue.
Thunderdrum T Level 4
The Thunderdrum is a large dragon that is as comfortable in and around water as it is on land. It is noted for possessing great power and a sonic blast for its breath attack
This dragon relies mostly on its two sets of wings, one primary and one smaller set to the rear, using them to get around and move through the water like a tornado. The Thunderdrum has legs (If you look closely in the book of dragons, you can see the legs.) Even though they are almost smaller and thinner than even a Terrible Terror's legs, they can surprisingly hold the dragons weight.
According to the Dragon Manual, a Thunderdrum is roughly the same size as an adult Viking, though they are clearly far larger and is reclusive in nature, living in sea caves and dark tide pools.
Seashocker T Level 4
The Seashocker looks similar to a purple/blue stingray, however it has two heads and very large wings measuring 15m (50 feet) in wingspan with two small flaps in front of it. As a whole, the wings look very similar to oars. The dragon also has small spikes lining its spine and the top of its heads. Their dorsal fins are very sharp and dense, functioning as amazingly powerful blades that are capable of slicing thick sea ices and even the most solid floes. Its necks are incredibly short. The Seashocker hunts in pods, and uses sonar in order to hunt.
The Seashocker is one of the few species to utilize electricity as a weapon. Their electro-charged bites can take over even the largest enemies, and Seashockers' breath weapon is to shoot out volts of electricity, to stun prey
Because of electro-abilities, rather interestingly, electric eels are regarded as a closest relatives in terms of evolutions, making both of lightning dragons and fish to be feared from ALL other dragons
Bewilderbeast T Level 5
The Bewilderbeasts are the biggest of all dragon kinds known in Berk, even exceeding the Red Death. Today, only a few of these titans remain out there. They have not been abundant in numbers, but this is unclear whether their populations are small by nature or if they are endangered. On stats, they are stronger in attacks and heavier in build, but less agile than their fire-breathing counterparts.
The Bewilderbeast is a very large, spiky dragon with two big mammoth-like tusks and huge multiple wings. The front side of their bodies are covered with burr-like spikes, along with two lines of spikes along the eyelids, giving an impression of eyebrows. 'King's frills' can be seen on the occipital region. Their size appears to be slightly larger than those of the Red Death. Protrusions from the back of their head form a frill. Unlike the Red Deaths, the Bewilderbeasts are unable to fly as not having proper wings enough for flight, mostly due to their colossal body sizes. This makes one of the few weaknesses that makes this species vulnerable
The Bewilderbeast is truly the king of dragons. They are currently the most powerful dragon, and also being so far the largest of all known dragons. It is normal for them to have their own 'nest' and be protectors or guardians of smaller dragons nearby, and they are seemingly generous to take care of fellows in the nest. Generous individuals even chase around ceanic fish and gather like baleen whales to feed dragons under their cares. Societies well ruled by each Bewilderbeast has highly advanced organization constructions that work for goodness of every member of the communities.
On the other hand, however, they can force or enslave the other dragons even against their wills to do the Bewilderbeast's bidding. This feature is quite identical to what the Red Death had demonstrated, and the fates of the minions really depend on each Bewilderbeast's morality and situations. They are leaders of dragons, and are essentially living 'nature' themselves to preordain entire ecosystems; being gentle, 'father nature' or benevolent, 'natural disaster or storm'.
Shockjaw T Level 3
Shockjaw is a typical water dragon with a number of small flukes and neck with one large fin. It has large membranous wings that resemble fins. He is a blue-green color.
Instead of fire, this Tidal Class swimmer emits bio-electricity, from a gentle jolt to a lethal bolt! It can be quite the shock. The bolts it emits can be strong enough to take down an entire ship and its crew!
Sand Wraith T Level 3
A Tidal Class expert in camouflage that buries itself in the sand. It's a good way to surprise their prey...and avoid sunburn! Some of these dragons migrated to the desert centuries ago likely looking for food and courtship. These are called Desert Wraiths.
Tide Glider T Level 3
Picture unavailable
This graceful Tidal class drifter doesn't "swim" through the water, it dances! Its saliva is said to have healing qualities... but it is too skittish for anyone to find out.
Unofficial: (Original)
Sapphire Waverider T Level 2
These friendly and playful dragons both swim and fly. They've also found a medium between the two, flying just above the surface of the water, often jumping into and out of the water. They have lithe and agile bodies. They're color is always some shade of blue, tending to be sapphire or ocean though.
They don't have scales, but their skin is strong and leathery. They bear fins and fur along their body. Their eyes are always either red or orange. They're very friendly, often playing games with each other in the waves. They are easily trainable, but don't like saddles, so riding bareback is best.
They are fierce fighters as well, and loyal to their friends, or trainer. They love food from the sea, especially crustaceans and kelp. They often have competitions with others of their kind as well, They don't like hail or sharks, as both are irritating, and they're terrified of storms as they could be shoved under the surface, never to return again. They are easy to befriend, and quick learners. Though the young ones learn quicker, so it is better to find one of young age rather than old.
