GameDadZ wrote:Deathwatch shoots marines. They want to use a discipline for helping to wounding on 3+. Can the marine player now use trans human physiology or do they have to declare using it as soon as I choose them?
It depends on the Deathwatch ability you're referring to. I don't know which one you're talking about to know when it's eligible to be used. If you have to use the Deathwatch ability at the beginning of your turn, you have to declare first. If you have to use it when choosing a target, you have to declare at the same time, and use sequencing - usually this means you'd declare you're using yours, they'd declare they're using theirs, you'd decide who gets to resolve first, and then you'd have to check the rules to see which has precedence if either.