Marcus' Farm Fox

Hello~ Just going to make this beast now:

Name: Kit
Tier: D
Type: Normal
Species: Fox
Appearance: Kit was found with a single tail, however as it grew Marcus saw there was some sort of mutation - two more tails. Her fur is orange with a white underbelly and white on the tips of the tails. From nose to the tip of her tail she is 60 cm in length. Kit stands 22cm tall.

Beast Traits:

Trait Name: Basic Evolution
Trait Tier: D
Trait Requirement: N/A
Trait Description: As this beast becomes older and stronger it evolves its strength.
Trait Effect: Every tier after the first tier Kit grows 2 tails. Once it reaches 9 tails, this trait will change to its final form. Aside from the growth of tails, its body evolves to a more complete and harmonious form. New traits may appear that may not have been possible prior to its increase in strength.

Trait Name: Greater Intelligence
Trait Tier: D
Trait Requirement: Only beasts may take this
Trait Description: The beast with this trait exhibits greater than usual intelligence, which grows as this trait grows.
Trait Effect:
Kit is able to understand more complex commands with less requirements to training. When ranking up Beast Taming or when ranking up Kit, the topic does not need to include as much focus on the training regimen of the beast. This is because Kit is able to supplement the intentions of Marcus with her intelligence and make decisions on her own that will help her grow.

Trait Name: Heat Control
Trait Tier: D
Trait Requirement: Beast only
Trait Description: This beast was born with the ability to modulate the heat around its body.
Trait Effect: Kit gains access to heat related techniques, as she is able to produce and manipulate heat close to her body.

Your first two traits seem fine. The first trait is rather interesting to me. It seems like you're going for the idea of using trait points and building the trait up over time to be better. If you wanted to use it to get access to other traits you don't need to. You can just use other traits points when your beast is higher tier to get the traits you want. Unless the idea you're having is for the tails to have passive or active effects at higher tiers?

Either way, I'm interested to see where you go with that. The second trait is good as well, interesting use of a trait to make ability drawbacks weaker.

The third trait you have is a bit confusing. From the sound of it, you just have a trait to produce heat or fire from your beasts body. If that's your point then you can just list it to say that this beast gains access to the use of fire or heat for it's abilties.

For the first trait I plan on making it so that as it grows more powerful it's able to use different elements in conjuncture so that they can create stronger abilities. If I only have a D-Tier trait for heat techniques, wouldn't that limit the level of the technique to D-Tier? But at the same time, wouldn't having multiple elements be a bit much? So I figured as a drawback to having a lot of element access, I would create another trait that took up extra trait points and simultaneously explain how its able to gain access to these new elements down the line.

Each new element would have its own trait associated to it.

The first trait would allow these elements to co-exist in a single technique - wind and heat would allow the technique to reach C-Tier, and have a higher range (fanning the flames) or wind, heat, life and lightning would be able to reach B-Tier (life to create a source of firewood for heat, wind to fan the flames, lightning entwining with the flames to become more powerful) etc. etc, but alone they would only have minimal effect (D-tier).

Maybe down the line, if I manage to get the beast to become a legend beast, I might have an omega tier trait that increases the base effectiveness to C-Tier instead (with a maximum of A-tier after combining with other elements).

Your heat control trait has to be C-tier and make sure you hav the organ that will produce it. You can say it got a natural organ that can produce some kind of heat :)
The other seems fine for me

Also, I will have to inform you that beast cant have access to use a magic or more like what you are planning to do after the fox got additional tail. It has to come from the beast naturally, such as having the organ to produce an element.