one–trick pony noun
plural ∼ ponies [count] chiefly US, informal 1 : someone or something that is skilled in only one area
▪ As a knitter, I'm a one-trick pony: I can only knit scarves. 2 : someone or something that has success only once
▪ a musician who was a one-trick pony and then faded away
▪ As a knitter, I'm a one-trick pony: I can only knit scarves.
▪ a musician who was a one-trick pony and then faded away
