A dominated creature got hit with a Terrified Retreat recently. It was already cornered, so I had it use its 5th level dimension door to flee. I'm not sure if this should have worked, and it was especially relevant because it was playing host to an Immortal Ichor it would have been abandoning. (I decided that because the Ichor was attached to this thing's blood stream, I'd let it count as one creature and escape with it.)
In retrospect, I think the best way to resolve it might be to have the Fleeing condition trigger a new save through Dominate's "obviously self destructive" clause. On a successful save, the creature flees and probably breaks the control. On a failure the controlled condition wins out, and the creature would be frightened but not fleeing.
What do y'all think?
I would read it as controlled taking priority.
Fleeing reads; "On your turn, you must spend each of your actions trying to escape the source of the fleeing condition as expediently as possible (such as by using move actions to flee, or opening doors barring your escape). The source is usually the effect or caster that gave you the condition, though some effects might define something else as the source. You can’t Delay or Ready while fleeing."
Controlled reads; "Someone else is making your decisions for you, usually because you’re being commanded or magically dominated. The controller dictates how you act and can make you use any of your actions, including attacks, reactions, or even Delay. The controller usually does not have to spend their own actions when controlling you."
Since the controller is the one dictating which actions you take, it would override the fleeing condition in my reading (The "you" in Fleeing is no longer the one choosing how you spend your actions, the controller is).
Making the fleeing condition trigger an additional save against domination would be a reasonable call, I would say.
I think you played the priorities correct; Fleeing supersedes Dominated.
It'd be odd to want to be Dominated (perhaps by an ally) to become immune to Fleeing, and also I think on a woo woo metaphysical level domination changes one's intentions while fear overwhelms one's ability to act on one's intentions (changed or not). One's taken over the conscious mind while the other has triggered the primal mind to ignore the conscious mind.
I don't think the self-destructive clause would be activated, at least not by the condition. Perhaps if given a new order which with the condition then seems self-destructive (due to immense fear of executing that order). Again perhaps, since I haven't yet imagined a situation where I'd rule that way.
That's an interesting situation w/ hosts inside other bodies during a Dimension Door (et al). A dev mentioned months ago looking into having familiars travel along though I don't recall any updates saying so. If familiars can, then certainly host-parasite combos could. I'd say you made the right choice there too, mechanically as well as for story reasons, though it might lead to odd situations where a creature has Swallow Whole and flees w/ PCs. :) Yet no, maybe not then though possession's a whole new level of integration. When targeting choices get blurry, then it seems the creatures have become singular enough.
Comedy answer: because being terrified isn't a physical effect, the "you" in Fleeing now refers to the controller, who uses all of their actions to run away (either with the controlled body or their actual body depending on how it works, potentially causing the controlling effect to end).