In the background of the art of Elvish Branchbender, you can see the elf's victim, a tree that has taken on a twisted life as a result of the nettlevine. Other treefolk would be horrified by such a vinebred creature—it has not undergone a true Rising (the process by which a tree gains sentience and motility to become a treefolk), but is instead an unnatural mockery of a treefolk.
Nettlevine is also, eventually, lethal for the afflicted victim. In the art of Nettlevine Blight, we can see a vinebred treefolk suffering the lethal effects of the controlling vine.
The card Scarred Vinebreeder represents what happens to an elf who has afflicted himself with nettlevine. The parasitic plant will shorten his lifespan, but in the meantime, he gains immense strength.