I made yet another Homebrew, Quaxels, are they balanced?

Question

Okay, I'll keep this one short by leaving out the fluff of history and such. Soo.. here it is.

Quaxel Traits

Ability Score Increase. Constitution +2, Strength + 2, Charisma - 1

Alignment. Quaxels are typically of a chaotic alignment, and they are sometimes drawn to evil by their monstrous origins

Age. They mature at age 100 and live usually into immortality. The oldest living Quaxel was age 280,383,284,245 years old.

Size. Standing 4'4 and weighing upto 450 pounds due to extremely heavy armor, your size is small.

Speed. You have a burrowing speed of 30 feet, and a walking speed of 30ft as well.

Heavy Natural Armor. Your AC is 18, Regardless of your dexterity and equipped armor. This is responsible for 3/4ths of your weight.

Change Appearance. As an action, you can transform your appearance or revert to your natural form. You can’t duplicate the appearance of a creature you’ve never seen, and you revert to your natural form if you die.

Acid Resistance. You are immune to acid damage.

Acidic Breath. You can spew out a 10ft cone of acidic breath. Everyone inside of this cone must make a d20 constitution save or take 1d8 acid damage or half as much on successful one. This damage increases to 2d8 at level 10 and 3d8 at level 20.

Frightful Appearance. You have advantage on intimidation checks, but disadvantage on persuasion checks.

Languages. You can speak, read, and write Abyssal and Undercommon.

Monster Origin. You count as a monstrosity when determining how spells and effects that depend on creature origin effect you.

Answer 1

Are they Balanced? No.

ASI: +2, +2, -1. That's an odd combination, since penalties to ability scores are very rare in 5E, and is definitely set up to favor Fighters. It is on the high end of the accepted range, making it fine by itself.

Age: Kind of ridiculous since any universe that includes Quazels is automatically at least twenty times as old as the real universe. For reference, reality is approximately 13,772,000,000 years old.

Size: 4'4" and 112 pounds (ignoring the 338 pounds of natural armor) is really big for Small size. Recommend changing this to Medium, with the same reasoning as Dwarf.

Speed: 30' for a Small race is quick. For a Medium race it would be fine.

Heavy Natural Armor: So AC is 18, regardless of equipment, unless that equipment would be better. This is incredibly powerful, overrides a number of class features, and would be sufficient special abilities to make Quaxels a desirable race for fighters and barbarians all by itself.
As several comments noted, this ability needs to be clarified if it is an Unarmored AC.

Change Appearance: Why would the race need to "revert"? That implies that appearance changed in the first place. But there is no ability to change appearance. This ability does nothing, as written.
If it works as implied, granting the race alter self for no spell slots and at will then it is an incredibly powerful racial infiltration ability. As the race's sole feature this would be sufficient to be worth playing. But wait, there's more.

Acid Resistance: Misnamed, since this grants immunity and not resistance. Damage immunity is too powerful for a racial ability.

Acid Breath: A 10' Cone of d8 damage is really weak. And the progression is way too slow. Too weak to be worthwhile, though one more straw on this camel's broken back.

Frightful Appearance: Good ability. Some positives, equivalent negatives. In general, this one is power neutral, though highly desirable for certain character types and play styles.

Languages: A player race that doesn't get Common! That's a bad idea. Bad, bad, bad idea. Characters need to be able to communicate with each other and forcing the Tiefling character to be translator for the Quaxel is going to cause hurt feelings and unneeded tension among the players. Which isn't fun.

Monster Origin: So, you're not a Person for spell targeting. That's a power boost.

Conclusion: Way, way too powerful. Also, too confusing.
Heavy Natural Armor and Change Appearance both need lengthy rewrites and clarifications before they can be playable. The implied effects are individually good enough to be an interesting and powerful race - having both is like getting to fully level in the Rogue and Barbarian classes simultaneously while everyone else only gets a single class. It's just too many really good things.
Acid Immunity is too good while Acid Breath is too weak. Added onto the previous two abilities, this is gilding the lily.
Frightful Appearance is an interesting and internally balanced ability.
Languages needs to include Common or the race isn't playable except in a joke campaign.
Monster Origin reads like you expected it to be a weakness when it's actually a powerful buff.

Answer 2

Maybe balance is not what you want

This is a totally left-field answer, but that might be appropriate since so many of these race homebrew questions are too.

So far, all of the homebrew races you’ve posted for feedback, under your various accounts, have been very unbalanced. Do you actually want balanced races? You don’t have to want balance! The examples so far indicate that you’re much more interested in novel, alien races that are not balanced.

Why not stop trying to balance them?

There are many RPGs that don’t care about balancing the power of player characters, and people enjoy them just fine. Rifts, World of Synnibarr, Burning Wheel, Traveller, Hârnmaster… there is a long list of RPGs that just don’t care about balance the way D&D usually does about races and classes, and are a lot of fun.

Your race concepts would fit right into any of those game systems and function fine.

Balance just does not seem to be important, since most of the race concepts you’re aiming for are inherently imbalanced, so maybe it’s time to step back and reconsider the assumption that your game needs to prioritise balance ahead of your fun concepts.

Baseline D&D 5e aims for balance, but it has to work for hundreds of thousands of players around the world. Your homebrew only has to work for you.

So long as your players are enjoying their weird and wonderful PCs, and you’re not hoping to publish these for other groups who are wanting balance, who cares if they’re balanced?

D&D 5e is very flexible. For your home game full of dozens of strange races, maybe balance is not important.

Answer 3

Lets evaluate this using DetectBalance, a tool that compares homebrew races to phb ones. Races typically have scores ranging from 17 (human) to 47 (Yuan-Ti Pureblood).

ASIs: 14. Slightly worse than the Mountain Dwarf, this is fine.
Natural Armor: 12, extrapolating from the Tortle's 9 points for its natural armor.
Change Appearance: 12. This is a level 1 spell with high utility at will.
Acid Immunity: 6. Yuan-tis are immune to poison, which is more common than acid.
Acidic Breath: 6. Very weak, but you can do it at will.
Frightful Appearance: 0. Cancels itself out. Languages: 1. I assume you forgot to write common.
Monster Origin: 2

Total Score: 53
And this isn't including the burrowing speed, which is completely broken for a PC to have. You could just leave any combat by just digging straight down.