Entremets are typically assembled upside down, meaning that the cake portion, which is the base of the entremet, is the last thing to put on while assembling the entremets.
The “body” of the entremet is typically the main flavor/component, since it will hold all of the other components together; therefore it is the first item to be piped into the mold. The mold, as well as the sheet pan that will be used hold the entremet mold, should be frozen before piping anything into them, to prevent melting.