Order of events

[BadLuckIrish]

What works first {Necrogen Mists} or {The Rack}?

[loop-s-pool]

Opponent decides which order.

[BlackJester]

What works first {Necrogen Mists} or {The Rack}?

Technically the controller of both effects chooses.  If they are controlled by different players, then Active player (the one who's turn it is) puts their stuff on the stack first, then around the table in turn order (or just the opponent for 1v1).