If an ethnic Cantonese sorcerer summons
mogwai evil spirits as tulpas made out of magic and thought-stuff, what are good weaknesses for them?
The sorcerer is not influenced by the Gremlins movies, but some similarities creep in due to the use of local thought-stuff.
If these are in some way evil fey, they should be vulnerable to iron. I think that's possible, but other possibilities include silver, gold, copper, jade, ash, salt, certain woods, certain herbs or more than one of these options.
What would best suit Chinese/Cantonese culture?