Before reach was reach, it was "can block as though it had flying." This would let you block such creatures.

Your opponent is not responsible for reminding you about your triggers--they can if they want to and/or they're nice, but they don't have to. (They can't let anything else pass, just missed triggers.) You cannot intentionally miss your own triggers--that's cheating.

If a player misses a trigger and you want it to happen, or you suspect it was missed intentionally, you can call a judge. Depending on the type of trigger, the action it calls for may or may not happen; the player who missed the trigger will only receive a penalty if it's considered generally detrimental or if the judge believes they're missing it intentionally. (The two have radically different penalties.)

Can you give an example of when an opponent misses a trigger, I call a judge over, but the trigger still doesn't get resolved?

How about when that situation occurs and also the trigger is not considered generally detrimental?

Would there ever be a situation where you had to prove the opponent was intentionally missing a trigger?

You notice that your opponent's Yeva's Forcemage should have triggered last turn--the duration of the effect would have already expired, so it doesn't happen. Or most triggers after more than a full turn cycle has passed since they were supposed to trigger--if it's been too long, causing the triggers to happen tends to just damage the game even more than it already is.

It's actually much easier to list when your opponent's missed trigger will happen:

• There's a default action linked to a choice the controller was supposed to make. (X happens unless you do Y...) The default will happen--your choice of now or at the beginning of the next phase.
• It's a delayed trigger that changes the zone of an object. (Exiling Geist of Saint Traft's token.) Again, your choice of whether it happens now or at the beginning of the next phase.
• It's been less than a full turn cycle, the duration hasn't expired, and you, the player's opponent, want their trigger to happen. It's put on the stack. (Some caveats apply about what it can do--if it tells them to sacrifice a creature, for example, they can't sacrifice a creature that wasn't around when the trigger should have resolved.)

All of what I just said above applies no matter whether the trigger's detrimental or not. The only thing that the trigger being generally detrimental or not affects is whether or not the Judge issues a Warning.

No. If you suspect that your opponent's doing that, you can tell the judge of your suspicion if you like, but that's as far as it goes.

If the judge believes your opponent is missing their triggers intentionally and that they know that it's against the rules to do so, that belief is enough to issue a DQ. Judges don't need proof.

They weren't actually bizarre--they were just a more complicated attempt to reach the same result. The problem was that many, many people didn't properly understand them, leading to strange results.