Actually, this mask was quite serious.
It is well known that Xuanwu's head isn't a turtle's head; it's a dragon's head. This mask is an abstract simplification, a turtle shell pattern with a dragon face on it, and the expression on the dragon face is very stern, even somewhat cruel.
If a member of the Four Symbols Sect saw it, they might be terrified, knowing this represents a Supreme Demon Venerable who guards steadfastly as a rock and erupts with unparalleled ferocity.
But knowing already that it was San Niang, it just looked like a turtle with a head on top. Zhao Changhe really wanted to pick up a pen and change that dragon head into a grinning Jenny. That would be more fitting for the character.
"What's that look for?" San Niang waved her hand in front of him, "Oh no, don't tell me you're aroused by just seeing a mask? Such a delicate flower."
