Yfa's Mama, as shown on the Cast page:
Of course, her real name isn't Mama, but her actual name is not revealed here.
Mao thought all the Gods died long ago, which is presumably common belief (Fahrin also details how the Darkness God died later, so many of the Gods probably are dead for reals):
But as Kalliv mentions, the Tree of Life hasn't withered yet, therefore Old Tjikko must still be alive:
Trèfle later also mentions that Old Tjikko lives at the Tree of Life:
So people outside of the Forest Clan believe she is dead, despite people in the Forest Clan believing she is alive. Of course, it would be evident to everyone that she is alive if people still encountered her, so presumably she is either rarely/never seen, or rarely/never recognized. If she is living in a different form to her usual, then it would of course be much harder to recognize her.
I posit that Old Tjikko is living in the form of a beast, as Mama.
Everyone refers to her as Mama, rather than her actual name (Old Tjikko), as she doesn't use that name in her current form:
Like how the Tree of Life would wither in Old Tjikko's absence, Old Tjikko (Mama) would wither in the Tree of Life's absence. And so, she returns to the Tree of Life to live there:
Bae understates how strange her family is, with the children being the offspring of a Spirit and a "Fruit Fox":
The strangest part of course is that Spirits are Not Born That Way. Spirits are born of emotions (links here later) or from a Spirit dividing itself into separate Spirits, rather than by any normal reproduction methods. Fruit foxes presumably do reproduce similarly to irl foxes, which is vastly different to Spirit reproduction. They should be thoroughly incompatible, right? So, something unusual has to happen to have a half-Spirit half-Beast child.
Chris explains that "a ritual to create life was needed for the pregnancy" and "There isn’t a lot of half spirits because it’s a lot of work". So some sort of magic was involved in order for them to have children, that is only ever rarely used.
The Spirit aspect of reproduction - "Papa has to literally give pieces of himself away" - still applied here from Papa's side, as well as a pregnancy (which I've been reliably informed is hard work irl) from Mama's side, so clearly things would have been a lot of work even before compounding that with a magic ritual on top of that to make it even harder.
But then consider that "There’s 5 of them in this family alone because they really have a ton of love and really wanted to make it work" like wow, first of all they must really love their kids to go through all that for them, but also, something so hard to do normally once would probably be much easier to do five times if one of the two involved was a God!
Yfa also gets a strong feeling that he has to visit the Tree of Life upon seeing it - a strong enough feeling that he is fine to put off searching for Yokoka (who he'd been trying to find for months, after she disappeared following her fight with Hurricane):
I think Yfa was feeling that his Mama was missing him (he'd been lost in Betel's Forest for two years); it would make sense for him to be as overcome with a feeling of wanting to return to her from such a distance if she had the power of a God!
Yfa also very quickly regained his vibrant palette within a few days of returning to the Tree of Life and eating his favourite blue heart-shaped apples there. And also... gained the ability to use plant magic without anyone actively teaching it to him:
We've seen other people learning (and failing to learn too) magic before, but this is different in that he pulls it off with no advance warning or practice, no incantation, and it's an entirely different type of magic than he's used before. While maybe this could be a more innate/natural type of magic (like shapeshifting for instance) than other forms spellcasting, it's also worth mentioning:
Kalliv specifically mentions that Old Tjikko "lends us her powers", and this new plant magic being power lent by Mama would explain how Yfa mastered it immediately. It also matches the element of the Forest God, and she would've been in the perfect position to grant that power to someone living in the same home as her for a while, and of course would want to do what she could to help protect her son leaving on an adventure.
It's also worth mentioning that there is precedent to lending powers to someone else, Copy lets Fahrin borrow one of his eyes, though as Mao notes "people don't work like that", and while he calls it a spirit skill, even spirits don't usually work like that, but it's probably pretty trivial if you have the power of a God, as Mama does!
Relatively minor note compared to the rest, but still worth mentioning: Kalliv refers to Old Tjikko with she/her pronouns for the entirety of his explanation about her.
And off course, this matches up with Mama's pronouns:
Further evidence comes from older concept art of the Forest God. Of course details may have changed between this being made long ago, and Old Tjikko's lore and Mama showing up in the comic itself (and non-comic sources are not considered comic canon), so this is only supportive evidence rather than fact:
Of note is that while the Forest God here is depicted as a hybrid of deer and fox, she can appear as more fox. And Mama, of course, has taken fhe form of a fruit fox. The plantlers sometimes being pictured as different plants also matches up with fruit foxes having preferences for and aspects of different fruits.
Visually, the colour scheme is also very similar:
At the top is the Forest God concept art, on the left is an early Mama design (strawberry fruit fox), and on the right is Mama's current design (grapefruit fruit fox). The slices of the wheel in the middle are taken directly from colours in each design.
