Correct line of action while observing illegal actions/plays

[bleakill]

Consider this situation. I am one of the few, or the only one observing an ongoing game. A player puts Samurai of the Pale Curtain (WW, 2/2, Bushido 1, If a permanent would be put into a graveyard, remove it from the game instead.) and points out its rfg ability to the opponent. An opponent then plays Ancestral Recall at some points in the game, while the Samurai owner points out that its ability would rfg the ancestral as well (obviously wrong), making a remark that it is "to prevent it from being played by  means of yawg.will" or something of the sort. Now, by the way that was actually played out/said, I'm convinced that neither of the players were aware of the Samurai's ability not removing the anc. from the game.
Given this situation, what would be the most reasonable way to restore the game state without me interfering (I'm assuming I can't simply point out the mistake as an observer)?

[Anusien]

Call a judge.  As a spectator, you're not allowed to interfere in a game.  Even if you have the best of intentions, you're likely to accidentally include too much/too little/wrong information and risk Cheating - Outside Assistance Penalties.  The only thing a spectator can do is go get or call a judge.  Do tell the judge all relevant information, and if it risks Outside Assistance (like revealing the contents of hidden information), take the judge away from the table.  As a spectator though, there is no reason to ever talk to players in a match.

[Almighty]

Similarly, Let's say you witness someone mistakenly search out a Mountain with their Windswept Heath(G/W fetch). It dawns on neither player that they can't do that and if not corrected immediately, could potentially screw up the game. Is protocol always the same in extremely obvious situations like this?

[Anusien]

Yes.

From the Universal Tournament Rules:

14.   Spectator and Press Responsibilities
Spectators are expected to remain silent during matches and are not permitted to communicate with players in any way while matches are in progress. Players may request that a spectator not observe their matches. All such requests must be made through a Judge.

Spectators and members of the press who believe they have observed rules violations should inform a Judge, but must not interfere with the match.

[bleakill]

I understand that I'm not supposed to interfere, but wouldn't calling a judge and talking to him in private potentially prolong the already erroneous game state?

[Anusien]

I understand that I'm not supposed to interfere, but wouldn't calling a judge and talking to him in private potentially prolong the already erroneous game state?

I think you significantly overestimate the amount of time it takes to get a judge and say, "That player fetched a Mountain with their Windswept Heath."

[andrewpate]

In my experience though, judges are extremely reluctant to act on it.  Every time I have done this, the judge has looked conflicted and then decided not to intervene, usually indicating something to the effect of it being too difficult to tell exactly what happened this long after the event, especially given that neither player even noticed.  Their attitude has seemed to be that even doing this is just meddling and that they'd prefer I just not do it.

[Anusien]

Seems like a problem with a judge.  The rules are fairly clear.

I can tell you as a judge it can be difficult to interrupt a match and figure out a complex issue that neither player noticed on the word of a spectator, but something like fetchland->wrong land is easy to verify.

[Clariax]

What Anusien has posted here is 100% correct.  The spectator should get a judge and should not interfere in the match in any way.  Is it possible that the judge will not do anything about the situation?  Yes, but that's no reason not to get a judge, and certainly no reason to interfere yourself.  Also, no matter how obvious the situation looks, it's possible the spectator may be missing something, it's also possible that by interfering, even in a seemingly obvious situation, something might be said that shouldn't be, that might direct a player to something he otherwise may not have been aware of.

Another detail to keep in mind, what you're witnessing may even be cheating, and by either interfering yourself, or failing to inform a judge, you may be assisting a cheater in their cheating.