Straightforward. MTG rules, so you know it works.

Magic the Gathering’s target-as-adjective is always useful, but often baffles people who haven’t played it. I don’t know what the general overlap of Nomic/Magic players is (I did enjoy Magic’s 2014 “vote” mechanic a lot), but it’s unlikely to be 100%.

Since it’s really only the Retreat action that uses the adjective “target” in a way that needs clarifying. We could just reword that action.

(Hmm, that link got stripped. Here’s a working version.)

I don’t really like the “target” terminology – I was the owner of a Magic the Gathering deck for a few weeks, fifteen years ago, but never really got into it – and I agree with Kevan that the problem here is the Retreat action. Consider this:

The effect of the proposal above would be that a Retreating Adventurer would still be affected by the Battle Actions “Fire”, “Befoul”, “Terrify”, “Teleporting Strike” and “Unbirth”, which rather misses the point of retreating from battle, namely running away from danger. Do we want all these Actions to have such an effect? Taking into account the massive 50 HP loss caused by Teleporting Strike, one might have expected Retreat to be more useful than this proposal makes it. Personally, I’d rather keep only Teleporting Strike, maybe one or two more.

So my counter-proposal is to reword Retreat as follows: “Until your next Battle Action, you may not be affected by Battle Actions.” We could add to this “You will still be affected by Battle Actions if their effect specifically extends to Retreating Adventurers”, but I actually think this will happen anyway for any Battle Action that specifically targets Retreating Adventurers (like Teleporting Strike) or explicitly state “including Retreating Adventurers” in its description.

(The current wording of Teleporting Strike leaves it open to conflicts of scope with Retreat: the former specifically targets the latter, and the latter specifically invalids attacks that specifically target an Adventurer who happens to be Retreating. Card’s proposal seems to fix that, but so would mine, by removing “target” from the Retreat description and thus making it more general in scope than Teleporting Strike.) 

Improved version of my above proposal here.