As in, which comes first? Active player's choice? To me, Forced should happen first, before anything, but can't find any backing for this.
Say you have Bule, Lord of Pus (Forced), Rat Ogres (Action) and Cloud of Flies (Triggerable Constant). All are "at the beginning of your turn", which these days is Phase 0.
Really an example of non-combat damage. A better example would be saying an Action can be played in response to Nurgle's Pestilence's Action, but not Thyrus Gorman's Forced effect (if that's the case, which i think it is)