枪手 (a hired gun) is a talented person, who is hired to perform a task of his strength to benefit the person who hired him. He will then collect monetary reward agreed by the two parties but the credit (reputation) of the good work.
The deal is usually illegal, such as "代考" - taking examine for the other, or an embarrassment to the hiring party if ...
枪手, or "gunman / gunslinger", comes from an allegory, (meaning a visible symbol representing an abstract idea), of the American "Wild West" where gunslingers, as legends go, went around the "young & wild" country in fast draw gunfights.
Sometimes these gunslingers were hired to fight someone else's enemies, i.e. as "...
他们说他写歌词找枪手 = they said he wrote his lyrics using a ghostwriter
枪手 is still mostly referring to '代人應試者 (substitute test taker)' nowadays but is often referring to substitute for any other task as well. In this case, it is a ghostwriter (代笔)
It is alright to hire people to do a job in your stead, but ...
丑 has these meanings:
ugly - 他長的好丑(醜).
disgraceful - 丑(醜)化, 丑(醜)事, 丑(醜)聞.
In the above usages, 丑 and 醜 are interchangeable.
clown - 小丑
2nd Earthly Branch - 丑时1～3点. (see note)
Note: Earthly Branch (地支) is an old Chinese ordering system. There are twelve Earthly Branches used to count time of years, months, and hours - 十二时辰：子时23～1点，丑时1～3点，寅时3～5点，卯时5～7点，...