They are of Wirewood, so they are Otarian and probably from the time the continent fell under the effect of Mirari's influence (which is probably the "mighty" thing that "stirs in the forest" as related by the flavor text, though it may also be read more bluntly as reference to a big creature). That turned several tribes and races into purer forms of themselves e. g. normal Soldiers like Gravel Slinger become faceless like Daru Warchief because the essence of the Soldier is to be less individual and their identity is lost to being part of an army, Clerics become divine light like Daru Spiritualist and Wizards like Scornful Egotist become magical flowing energy.
So what did the Elves become? They shifted closer to becoming part of their Forest and turned tree-like/plant-like/beast-like/primal/green in appearance like first Wirewood Channeler and eventually Wirewood Guardian.
But the connection to their Otarian origin doesn't stop there. This legendary is literally a Wirewood Elf: 1/2 green Elf that taps for a single green mana. But that's a card from the first set of the block, Onslaught when the mutations weren't that strong yet, so this mutating Elf's other part of the ability is a reference to the last set of the black, Scourge, which is named for the scourge of Dragons; those received support both in the form of tribal as well as a theme of high converted mana cost, especially converted mana cost 6 or greater as seen on Dragon Fangs, and an Elf buddy, Krosan Drover, from the other big Otarian Forest, but probably most famously on Fierce Empath.
So they don't quite become a Treefolk, but one of the tree-iest Elves you know.
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Knowing wizards I know it's most definetly not gonna happen, but if they really want Commander to be inclusive they should release the box at normal price. Imagine how many boxes would be bought. But since Wizards know we're all gonna buy it anyway, premium price it is =/
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