Sheets of ice fell off of the frost finch, but that wasn't because it was losing more of the held back energy and allowing the wind energies within it to fly freely through its bond with Grace. Instead, this was ambient frost and ice gathering on it because of the ice type energy it was focusing on.
The wind in the immediate area was also getting much stronger. Especially since the wind and ice crystals around them had been bled dry by this entire process.
The herbs were causing all of this. The herbs used for Grace and the frost finch had been absorbed by their bodies. There was no stopping at this point. But that was why this was a monumental achievement in a way. If the two had not reached this point, then they would be extremely ill or dead.
