Ancient Acidic 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 acid from their gullets, a natural substance that they produce from within just from eating, sending balls of extremely caustic towards their foes and future meals alike. When it comes to close combat, they use their impressive and deadly bite in tandem 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 acidic salamanders walk on four thick and muscular legs and have a very powerful tail, they are fast moving creatures on land and even faster in the water. For the purposes of hunting  prey, they launch a burst of highly-corrosive nearly boiling hot liquid from their gullets, The this hot acidic substance sticks to victims, melting 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 half melted by their bile. They will eat any meat they can, but seem to fish and other aquatic creatures.

There is a more common variant of ancient salamander that lives in spits a liquid jelly like highly flammable substance that lives in jungles, as opposed to swamps.
This variant replaces every acidic part of the ancient acidic salamander and instead uses a flaming pitch like substance in the same manner.  It is more common, but much more resistant to fire.

Physical Characteristics

An ancient acidic 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 all have larger fins 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 brown, black, and gray, but sometimes they come in shades of green or even yellow. 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.
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.