Probably vines, maybe also wooden branches curling around, maybe also have like an "infect" status that turns the princesses into Timberweres over time to achieve a Timberwolf-were transformation. I'll send links of Timberjack, the Timberwere Applejack I mentioned.
https://www.furaffinity.net/view/19388312/ https://www.furaffinity.net/view/22623454/