This Stone Skin spell had been cast back when they fought the treant. Its effects simply hadn't worn off yet.
Then the Beastmen charged out.
The reason Lin Yun hadn't noticed earlier was simply that it was too dark. Even with Dark Vision, seeing in the dark was much like looking through night-vision goggles, so he couldn't make out that the young lady's skin was slightly gray—the effect of Stone Skin.
Lin Yun wasn't the only one on guard. The young lady had been wary, too.
If Lin Yun and the others attacked, she had the Rapid Transformation feat, which would let her quickly transform into a Fire Elemental.
She could only become a Huge Elemental this way, not a Gargantuan one, but that was enough.
And just because she charged ahead didn't mean she was reckless. In truth, she was quite shrewd.
If she charged out, Lin Yun and the others would naturally be seen as "weak." The enemies would pick on the weak, mistake them for allies, and perhaps even try to encircle the enemy to save them.
Of course, she had no intention of saving Lin Yun and the others. There was "nothing in it for her."
As long as the enemies shifted their attention to Lin Yun and his group, she could make her escape.
After all, "Fire Elemental" wasn't the only thing she could turn into.
At level 10, a shifter could already take on three elemental forms. The only pity was... she couldn't fully transform into the other two the way she could into a Fire Elemental.
Still, even something like Elemental Form that let her "burrow" would be enough.
Besides fire, she also had earth and water.
She'd prepared water specifically to avoid some "awkward" situations.
In short, if a large number of