Mandarins are extremely difficult to keep alive unless they are trained to eat frozen foods. Otherwise they need pods
and LOTS of them. My guess would be that it starved to death. How long did you have it and what did it eat?
Shrimp typically don't attack fish. Some will try to clean fish, so maybe that was what was going on?
More info would really help...how long have you had the tank? What are your water parameters? When did you add these fish and how long did they live? Did any show signs of problems prior to dying? How do you acclimate them?
Also, what kind of wrasse did you have? Most smaller wrasses (fairy wrasses) need 50-90g, there are only a couple that I can think of that would be okay in a 24g (possum wrasses). Even 6 Line wrasses are best in a 30g+.