If I could go back and do things better, the fix would be to not have this situation be possible
So ideally we would want a simple ruling that makes the situation impossible, but doesn't change the way anything else currently works. I don't think such a thing exists.
Let's start by summarising how the situation arises. It's a combination of four factors:
- TR-alikes play an Action card multiple times by looking at the instructions on the card each time it's played.
- The instructions on three Action cards, namely BoM, Overlord and inherited Estate, change dependent on the location of the card.
- Some Action cards trash themselves when played, plus during the Action phase Crown can be trashed by buying Mint with Black Market or top-decked by gaining Mandarin.
- Once such a card has been trashed or top-decked, a sequence of subsequent Actions can cause its location to become unknown.
For it to be imposiible for the situation to arise one of these factors must be eliminated.
The third and fourth factors cannot be eliminated.
The second factor can only be eliminated by modifying both the way Inheritance works and the way BoM and Overlord work. Some suggestions have been made on each of these fronts, so maybe this is a possibility, but having to fix two types of functionality seems excessive.
To me the first factor seems the most promising one to eliminate as it only involves one type of functionality, though there are five cards (TR, KC, Crown, Disciple and Ghost) that use the functionality. The suggestions made so far on this front had the merit of preserving the way everything else currently works, but the disadvantage, as Donald has pointed out, of being somewhat obscure and confusing. Mine also had the disdadvantage that it would still have allowed a TR-alike to attempt to play a plain Estate.
I can see two other ways in which the situation could be rendered impossible by changing the way Tr-alikes work, but both cause changes to the way TR-alikes interact with morphing cards: BoM and Overlord would get to morph into a different card on each play.
Solution 1: TR-alikes read the text of the card once and remember it rather than looking at the card each time it is to be played, but would this require a change to the wording on these cards or would a ruling to the effect that this is what is meant by playing a card twice/three times suffice? Might this solution cause some uncertainty as to what the BoM/Overlord is after it has been played twice? For example after TRing a BoM as two different non-self-trashing cards is the BoM the first card impersonated (on the grounds that the second play of the BoM couldn't find itself to become the second card impersonated)? Or is it the second card impersonated (on the grounds that the second instruction to be a particular card until leaving play overrode the first instruction to be a different card until leaving play)?
Solution 2: TR-alikes are rephrased to be something along the lines "You may set aside an Action card from your hand. If you do, play it, then move it into your Play Area and play it again." This solution works by preventing the card from being moved until it is being played for the last time and has the advantage that it leaves no doubt about what the BoM/Overlord is after it has been played for the last time (on previous plays it wasn't in play, so reverted to itself immediately). It does, however, have the major disadvantage of being very verbose. While that's not a problem for TR or KC, it would be for Disciple and Crown.
Maybe neither of these solutions are acceptable, but I'll finish by reiterating that (a) any solution needs to eliminate one of the four factors that lead to the situation and (b) in practice that means either the first or the second factor.
Edit: added Ghost to the list of TR-alike cards.