多面手 A many-sided hand. A person skilled in many crafts.
十八般武艺 The eighteen martial arts. Originally the skill to use eighteen kinds of weapons. Figuratively, a wide range of abilities. A Yuan drama has the line: “Relying on my eighteen martial arts…”
万金油 Ten-thousand-gold oil. A balm of menthol and camphor for headaches and minor burns. It has many uses but cannot cure a serious illness. Figuratively, a person who knows a little of everything and has no specialty.
The balm’s name marks the limit. Breadth without any depth earns a mild insult.