The "rarest" are axanthic/melanoids and hypomelanistic which is especially rare especially if you add a copper mutation with any of the above, non albino golden axolotls on their own are rare, golden albinos with a copper mutation are actually rare but hard to distinguish but they'll always have red or pink eyes and have a peachy orange hue instead of a very yellow coloration but I do not know if anyone can say if they're any more or less rare than say a light axanthic often referred to as lavander or Dalmatians but a hypomelanistic melanoid is much more rare than a melanoid/axanthic/or albino unless maybe they're also copper then they're even more rare. Many say NAGS are still the rarest but hypomelanistic axolotls are far usually much more uncommon. Pied axolotls are also considered pretty rare more rare than just a copper mutation but some mixed breeds of these genetics make them more rare. For instance blue gilled axolotls are also quite rare and if they appear on a pied axolotl it makes it much more rare. Idk how NAGs got so expensive tbh considering they aren't anywhere near as rare as a blue gilled pied, or a mosaic /split mosaic. Which is essentially two different kinds of chimera in one case the egg is divided perfectly almost and gives them a perfect split one side of their body has one eggs attributes and genetics and the other half of their body will display the other eggs genetics, where as mosaic axolotls have two different sets of genetics but mixed up like someone took playdough and mushed the genetics together giving them a unique pattern with different genetics appearing randomly throughout their body. These types of axolotls are extremely rare much more so than a copper, melanoid, or any other mutation or any other morph as there is absolutely no way to breed these axolotls they are a freak accident. You will end up paying almost as much for a NAG in some cases as a mosaic which is a complete rip off. Blue gills are more rare than NAGs but for some reason NAGs are still considered rare. I beg to differ they just don't always live to adulthood, thus harder to breed. The other rare "morph" I don't even want to mention is firefly axolotls because they do not exist, they are never born like that, only a select few were changed in embryo to give them a different morphs tail, to study their regeneration. Those were then sold as pets when the experiment ended and some horrible people began cutting the tails off of fresh hatchling and sewing other tails on sometimes leaving the body of the less suitable axolotl to... pass in pain and even if they do live through such a practice I have a hard time believing they'll ever want to interact with humans again, and I totally understand that. But these horrible practices produce a supposedly "rare" *cough* MAKE BELIEVE morph.