Thanks go to Liv? for most of these questions. While some are out-of-character, I've tried to answer most of them in an in-character manner.
What is EF's stance on players choosing forms from other canons (eg. Moogles or totoros)?

Don't do it. Elysian Fields is meant to be an original setting so while we do draw inspiration from mythology and legend, we don't want to see chocobos or Pokemon running around.

How does a Therian's BMI affect their transformation?

Therians by nature require a lot of energy for their transformations and have a high metabolism as a result. There's really no such thing as an obese Therian (despite their ravenous appetites) because they're physically designed to burn off the energy their bodies have stored almost right away, and continuously.

Can Therians turn into any animal in spite of their location and natural habitat?

As long as a Therian has learned the animal's physical structure and its behaviour, they can assume that form regardless of their location.

Animals are, however, limited by their own strengths and weaknesses as well as their basic needs. A firefox would be a bad choice in a snowstorm, and likewise a fish would suffocate quickly out of water.

Are there limits to the size of the animals that a Therian can turn into?
Can Therians turn into dragons?

The biological structure of shapeshifters and normal animals means that Therians cannot significantly increase or decrease their body mass. They are able transform into animal forms as small as 6 inches or as large as 10 feet, but they can't go beyond that and the extremes of this range can be difficult.

There is also some debate among dragons and the Dracovari over whether a Therian could assume dragon form anyway, since dragons are considered to be a much more complex biological form than most other animals.

Can Therians turn into other sentient races?

No. Therians get their abilities directly from the combination of their animal and human DNA combined with (or by) the Bloodlust Virus. This limits them to forms that are tied to the animal kingdom.

Can their animal forms be a cross-breed between two different animals depending on their intentions?

Therians can't assume two different forms at once. They can, however, 'shift parts of their bodies into animal form while the rest stays human.

Are they free to alter animal forms?

While it's not uncommon for children to misstep when transforming, they're often ridiculed by their peers (and non-Therians) for getting it wrong. This puts a great deal of pressure on Therians to mimic their chosen animal perfectly, especially as adults when they should know better. No Therian raised traditionally would willingly customise the colours of his animal forms.

However, the markings a Therian has in human form can sometimes transfer with them into their animal form, so a red-headed Therian form may well have a slight red tint to white fur.

Do Therians choose animal forms according to personality?

Personality doesn't normally influence their choices to a noticeable degree except where their personality influences their needs. That said, they do tend to choose animal forms that suit their lifestyle. A Therian who has to be fast will normally choose at least one form that enables him to sprint while a Therian who needs to travel great distances on a regular basis might choose a bird.

Is shapeshifting physically damaging?

Yes, it can be. Torn muscles and broken bones can can happen if a shapeshifter attempts to morph too often or stay in their animal form past their limitations. Fatal accidents like these can also happen if a Therian attempts to assume a form that's beyond their current capabilities?.

As some animals have venoms or musks to protect themselves, can Therians have these, too?

Yes. While in an animal form, the Therian essentially is that animal (with human reasoning and intelligence). They can do everything that animal can do. (Please note that Therians also share an animal's fears and weaknesses while in that animal's form, like a cat that doesn't want to get wet or a horse that will panic in a fire, but they're able to deal with such fears as humans might.)

Is there any specific illegal activity directed at Therians? !!!!!Has anything been done against mistakenly poaching Therians?

Elysian pets can be especially exotic since few people travel willingly (which means they may only see a few animals in their lifetime compared to what's out there) and there's always great demand for such. Poachers aren't known for their caution so it's natural that Therians might get caught in the odd trap, and children are especially vulnerable.

It's a surprisingly prevalent problem, but it is their problem and it's the biggest reason that Therian clans are so careful about patrolling and protecting their territory.

It's also not uncommon for city-dwelling Therians to go missing. Rumours abound of black-market trading in Therian slaves, some of whom are deliberately caged as pets. There are even stories that goods produced by Therians in animal form (like wool, milk and venom) are better than the normal fodder so some slaves may even find their way onto farms.

Can Therians, as animals, eat foods that are safe for humans but not for animals?

No. While in animal form, a Therian is physically susceptible to everything the animal would be. Therians also tend to eat whatever the animal would eat while in that form (so yes, flies if they're a frog).

If a Therian in animal form loses a limb that is non-existent in their human form, what happens?

Everything a Therian gains when transforming has to be “grown” out of what they already have so if they damage or lose a tail or a wing, those injuries will translate into their human form.

The result of this can vary depending on the animal, but it normally affects the closest body part in relation to what they've injured or lost.

Even with so much researching done, can a Therian really perfect an animal?

No traditionally-raised Therian would ever say they've truly perfected a form because there's always something more they can learn, and because their human reasoning means that in any given situation they may not react as the animal truly would.

However, they might say they've mastered a form if they can maintain its appearance and remain mostly true to its behavioural traits in even stressful situations. It really depends on the animal and the Therian in question. Some animals are much easier to learn while there are some that are just impossible to truly understand.

Do some Therians use their forms as a means to gain income?

Yes.

Has there ever been a Therian who could transform into an animal or creature they have only seen once?

No. Even Therians with eidetic memories can't possibly see a creature just once and then mimic it because the transformation is about movement and behaviour as much as the physical form. Animals tend to react and move differently depending on the scenario and those differences can make or break a form, which is why Therians need to spend some time observing the creature before they can make the attempt themselves.

Are Therians affected by migration and hibernation instincts?

Because Therians can't remain in animal form beyond their limitations?, they can't go into hibernation regardless of their animal form; once they're asleep, they just revert back.

However, hibernation does affect when and how often they can transform into an animal. If a bear form goes into hibernation, the Therian will only ever be able to fall asleep while in that form (which will automatically revert them back to human and make it a wasted effort).

Migration affects Therians, too. Though their human reasoning will make it possible to fight the instincts to travel, those instincts will be strong enough to cause problems whilever in that form.

Therians usually just avoid forms that are under such strong instincts during their hibernation/migration periods because they're usually more trouble than they're worth.

Do Therians have varying capabilities of transformation?
How are they viewed by their society if they take too long to master a form?

Like any other race, Therians vary in how quickly they can master a form, for any number of reasons. How people who are slow to master a form are viewed really depends on the reason, but it's their responsibility to find ways to catch up.

If they do their best and still can't catch up, they aren't treated badly but will still often feel shame, especially since they may be stuck doing the chores normally reserved for children and the elderly.

On the other hand, if they don't do their best, they'll often be teased or even shunned because their lag brings down the rest of the clan and they're “just being lazy”. If their lack of action causes problems for the clan, they may even be exiled.

If Therians mate in animal form, what happens to the child?

While technically Therians can mate with an animal while in that animal's form, the species has evolved to the point now where they're physically incompatible in terms of reproduction, since Therians always revert back to their human form. Even if that were not the case, mating with animals has become socially unacceptable except among the more feral clans, and as one of the more severe crimes would most likely be punishable by exile.

In a fight between a real animal and a Therian in that animal's form, who would win?

No matter how much a Therian practices their forms, they still ultimately think and react as a human would, so it's difficult to judge.

If you want to compare them strictly on the physical aspects of their form then most bets would land on the real version, since even Therians who have mastered the form will never be quite perfect at it.

However, it's really impossible to predict the outcome one way or another. Even if the Therian is physically weaker than the real animal, they can use their human reasoning and intelligence so may be more cunning.

Can a Therian be infected by a disease that only affects animals?

Yes. If they contract the disease while in that animal form, it can be translated into their human form when they revert just like injuries. In these cases, the disease is not normally contagious among other humanoids but may be communicable among Therians.

Do Therians end up losing a form as they grow?

To survive while using an animal form, Therians have to be as particular and perfect as they can manage, so if they don't practise a form for a while they can forget how to use or even assume it.

However, it's extremely rare for a Therian to be so unpractised that they forget the form altogether, and usually all they'll need (after the initial years of study, of course) is a “refresher course”.

Can a Therian revert to human form neglecting to change something back?

No. While transformed, they must concentrate on keeping the animal form in place, otherwise they revert to their default human form so it's not possible for them to neglect something like that.

However, it is possible for them to do the reverse.

How does the public view a Therian in a high religious or political position?

Well, to be honest it's rare for a Therian to land themselves a position like that. They don't normally subscribe to organised religions and even city-dwelling Therians aren't all that interested in the politics of the other humanoids. They actually tend to view politicking as being beneath them, since it's overly complicated and so far removed from the natural order and the Therian way of life.

This tends to lead others to view Therians as simple-minded, so in the rare event that a Therian does land such a prominent position they're often viewed by the general public as being incapable of doing the job well. Even if they have proved themselves perfectly capable, it's such an unusual occurrence that there'd be plenty of gossip and their every move would be publicly scrutinised.

Can Therians be Summoned by Nymphs?

Yes. While in animal form, Therians can hear a Nymph's summons, but the human mind of a Therian dulls it to a faint whisper. They can choose to ignore it, but most will at least respond to the Call of a Warden since that usually means trouble in the area that could affect the clan.

Is there a way to tell Therians apart from humans or their animals?

While in human form, Therians look completely human. However, their physical characteristics can set them apart from other humanoid races (e.g. height, build, hair colour, etc.)

That said, Therians do tend to pick up a sort of "wild" smell from their time spent in animal form.