"Quedarse moñeco" is an expression popularized by the spanish comedian David Broncano, comes from "quedarse muñeco" it's a way of saying that a person has died.
According to the own Broncano the previous steps to remain moñeco are "volcar" or fall, "amochar" or hit on the "mocho" or head and as a result "te puedes quedar moñeco".
In Twitter the account @SaQuedaoMoneco created in January 2016 compiles dates of the death of famous people.
@yu_ntpn ME HE QUEDADO MOÑECO. Escribo desde el tanatorio.— Antonio Castelo (@SrCastelo) 20 de enero de 2015