Here is a light starter of my own to give an idea what the disappearing Novotny is about.
1...Bxg6 2.Qf8 (Bg7?)
1...Rxg6 2.Qh8 (Rh7?)
Simple but satisfying none-the-less. The self-blocks are a common mechanism. The "disappearing" part of the Novotny, i.e., the reason that the threatened mates do not work is because of the loss of guard on h7. Two points that I would like to make about this problem. First the threats are separately forced. Second the mates after the captures of the key piece depend on the mutual interferences of the rook and bishop.
On to the heavy hitters with one of my favorite Dombrovskis problems. While this is not a Zagoruiko, it does have the feeling of one. Indeed, there is a set Grimshaw:
Then the key, which is strong because it pins the bB, set off some wonderful changes.
Notice how the bQ is used to make the mate 2.Bc8 "disappear" after 1...Bxd6.
Here is another famous problem by one of the popularizers of the disappearing Novotny. This problem won first prize in the BCM tourney and is often cited as THE example of a disappearing Novotny. The bK has a flight at c3 which is met by
The give and take key opens the lines of the wB and wR to threaten two wQ mates
A lot going on in this wonderful problem, but I want to point out some of the things I like about it. First there are several interactions of rooks and bishops. The key opens the wR and wB lines but closes the bR and bB lines. Sydenham calls this an anti-Novotny. However, the move 1...Kxb5 also opens the lines of bBa3 and bBa4 giving kind of a Black anti Novotny. So it has a true Novotny, a White anti-Novotny, and a Black anti-Novotny. Several people have mentioned the role of wRh3. It is used to provide for the set flight 1...Kc3, but it only has a minor role in one post-key variation to cover the square c3 after Bxb5.
This is one of my own compositions that I really like that sets the economy record for disappearing Novotny in style. 10 pieces with no pawns! Moreover, there is a nice changed mate from the set play, unique separation of the threats, a total defense, and a wonderful thematic withdrawal key.
Unfortunately, as with many #2s now a days the basic mechanisms were found to be partially anticipated by a Jac Haring problem (https://www.yacpdb.org/#468766). I still managed to shave 3 pieces off to obtain the record.
Here is one of my favorite problems and a little bit of a twist on the usual disappearing Novotny. Notice the wP on c4 stands at the intersection of the bR and bB. Moreover captures of this piece have set mates:
The key changes all of these mates with a variety of effects. It is worth close study to see why all of the mates are changed.
This problem is actually a combination of two Novotny ideas: the Norwegian Novotny where the white piece already stands in the intersection and the disappearing Novotny. This is excellent work but I would opt to put a bR on h3 to force the threat 2.Qd4 with 1...Rxf3, of course this is a matter of taste.
In my opinion this is a classic problem that deserves more recognition. The use of the wQ as a Novotny piece is rare and this is an excellent rendering. Here the Novotny captures are coupled perfectly with abandonment of rear guard, letting the wQ march right in to mate.
I like how the threats are forced by the same bB. Outstanding!
Here is an excellent little Meredith demonstrating the idea with pin-mates.
Unfortunately the Qe5 threat goes unforced and I cannot see how to force it without breaking the Meredith economy.
Another delight with a regular Novotny try and a disappearing Novotny.
Another Sydenham problem that I like. The formation of the ambushed wQ is very common in disappearing Novotny problems, but I really like the critical play. There two different pairs of threats but the disappearing mates remain the same.
This problem is the famous changed disappearing Novotny. One of two problems to show the idea and the other problem has an unprovided checkmate! (see here) It does have a flight taking key in part (b), but none-the-less a milestone.
(a) 1.Sdf3 (>2.Rc6,Rc1)
(b) 1.Sgf3 (>2.Qh5,Qg1)
Finally one of mine which is certainly in the running for my best problem. There is relevant set play:
That's right, a combination of the Fleck and disappearing Novotny theme. Overall this came together splendidly and I am really happy with it.