Ancient Salamander

 Said to be related to Zehirs, but taking a completely different evolutionary path, opting for a huge iguana like build, but still utilizing a similar hunting method. There is speculation that they are related in some way to dragons, due to them being able to understand draconic, but they also understand  lizardtongue even though they themselves are unable to speak either language. Many people do not believe this however, and simply chalk it up to them being 'clever'. Though one researcher came up with something related to some old forgotten god named "Lernaea".

Combat

In a fight, an ancient salamander will try to use its ranged capabilities before engaging in melee if possible. They fire balls of flame from their gullets, a natural substance that they produce from within just from eating, which ignites when it meets air, sending balls of fire towards their foes and future meals alike. When it comes to close combat, they use their impressive and deadly bite in tandom with their large claws  to rend and shred their enemies apart. If they are heavily damaged, they will go into a frenzy and try to quickly finish off their foe, and if they cannot be calmed down or healed in time, they may fight to the death if there is no other option.

Nature

Ancient salamanders walk on four thick and muscular legs and have a powerful tail, they are fast moving creatures whether on land or in water. For the purposes of hunting  prey, they launch a burst of highly-corrosive liquid from their gullets, a substance so volatile that it bursts into flames upon contact with the air! The burning pitch-like substance sticks to victims, burning them alive and beginning the digestive process.
They weigh close to one and a half tons, and must eat at least 100 to 500 pounds, averaging at about 250 pounds of meat a day, depending on their size.
They prefer to eat their meat cooked by their own flames. They will eat any meat they can, but seem to prefer lamb and venison.

There is a variant of ancient salamander that eats primarily fish that lives in swamps, as opposed to living in jungles.
This variant replaces every fiery part of the ancient salamander and instead uses acid in the same manner. It is rarer, and more resistant to diseases and poisons than a normal ancient salamander.

Physical Characteristics

An ancient salamander looks like a huge iguana, but with large head and neck-frills and back sails that provide a cooling mechanism, ensuring the cold-blooden creatures do not expire in the heat generated from their own bodies. These frills also help them swim, and many have large ones on their tails. While uncommon, some also have forked tails. The frills are usually a complimentary color to thee shade of their scales. They also have horns placed directly above their heads that are the same color as their scales, these horns grow larger with age.
Speaking of scale color, they can come in many shades. Most commonly they come in shades of red, orange, yellow, and green, but sometimes they come in shades of pink, blue or even purple. In extremely rare cases, they can even be albino, being shades of light greys or white. Whatever the case, their undersides are always a much lighter and paler shade, and the scales on their undersides are also much finer, appearing like a thick leathery skin. The color of their eyes seems to be random however, and can be anywhere in the rainbow. Their claws and teeth are both around 4 to 8 inches long, are are typically cone shaped, but serrated on one side. 

Taming and Training

Many humans have tried and failed to train ancient salamanders, doing so is nearly impossible without some sort of magical aid. If they are raised from a young age however, then with enough food and time, one can simply treat it like an overgrown dog, since they are easily as if not more intelligent than many a canine. Acquiring an egg can be very difficult, but those that are found can be sold for anywhere from 2,000 to 5,000 gold. Getting someone to train it for you would cost roughly 1,000 gold or more. 
The DC to train a young ancient salamander is a 21, and is higher for an adult, being around 27. Lizardfolk and dragonborn tend to have a much easier time training the adolescents and adult salamanders, unlike most of the humanoid races. For the purposes of this, when a Lizardfolk or Dragonborn/Half Dragon make a Animal Handling with an ancient salamander, they gain a flat +5 to their roll. Their scales alone outclass most light or medium barding, heavy metal and plate barding being the only outliers, though this slows them down (10 feet a round for both their walking and swim speeds). Though to some, the extra protection is worth the movement penalty. Many lizardfolk see it as dishonorable to the salamander, and instead bejewel their salamanders with decorative gold bands and piercings.

This is my attempt to bring the thing from total war to my dnd games, and others if they want to use this.