There is a few rules you might want to follow to not end up in a polytopia cringe compilation...
1. Keep them simple: Don't use disadvantages to add more advantages if you're making a special tribe. Aquarion doesn't have disadvantages! Bad example of special tribe advantage: All their units Regen 1 life automatically even if they used their turn. Nope, more like something like this: Their smithery tech is modified, it lets them make regenerators instead of swordsmen, ect.
2. Keep them fair: Your tribe cannot start with more than one techs, because they can't have disadvantages. No disadvantages means that instead of adding more stuff to a tribe and taking other stuff from it, you will have to stick to the Canon tribes' rules and make something classic. Again using Aquarion as an example, they only have 3 special units, their balanced giant which is a crab and not a thunder firing robot with laser eyes and 3 speed, their amphibian and tridention. Don't make OP units, don't make too much modified units either. A tribe with humans CANNOT be special, unless they come from the future or the past. A tribe which is normal CANNOT have special units or techs.
3. Keep them logical: Don't try making a Undertale related tribe. Not because I don't like Undertale, but because a idea like that would be stupid, immature and without any kind of effort and creativity. Don't give them two colors or a story and look that is completely nuts. Tribes are based off cultures, such as Sushang, based in Japanese, or Marinoo, which are aliens, but they are a stable and good tribe! If you don't want polytopia to turn into something cringy like FNAF, then try to follow these simple rules
The key to making a perfect, original, and good fanmade tribe? Ask yourself. "Would this tribe have the potential to be canon?" "Does this tribe have the classic Polytopia feeling?" "Would this tribe be OP in-game? How would playing with it be?" Follow these to make a good FMT