The ShowMoves problem appears to occur because this still uses the old highlighting routine. And now that I leave out the loop directive from the internal move descriptors this cuts non-final slider legs with m rights (which should continue after a succesful try) to their first step. I should make the highlighting in ShowMoves also be done with NewClick(); I guess I didn't do that because it never has to deal with a double locust capture, as hovering gives you at most a single potential victim.

A reasonably cheap method for tracking pieces (of all types!) would use an array location[] indexed by (colored) type, where the square numbers (calculated as 128*rank + file) where pieces of a given type sit would be stored in location[type] and location[type+512]. This can be updated in MakeMove() like

function TrackMakeMove(m) {
  var p = m[-6] & 1535; // moving piece (stripped of marker flags and virginity)
  if(location[p] == 128*m[1] + m[0]) location[p] = -1; // mark first entry as invalid when it was for the moved piece
  p = m[-1] & 1535; // promoted type (could be same as mover)
  if(location[p] < 0) location[p] = 128*m[3] + m[2]; // put destination in first entry when the latter was unused
  else location[p+512] = 128*m[3] + m[2]; // otherwise it must have been for the other piece of this type, so this piece uses second entry
  OriginalMakeMove(m);
}

and similar for UnMake(). It would not take account of capture of the pieces, (which would be cumbersome because of the possibility of locust capture), so when using the locations for a type it should always be tested whether a piece of that type is actually there; it could still indicate the square where a piece of that type was captured, but which now is occupied by something else.

Limitation is that it would only work if there are at most two pieces of the types of interest. Which for Suzumu Shogi would not be the case, as there could be four Tetrarchs. But somehow it doesn't seem wise to adapt a general feature to a very exceptional case; in virtually every variant there are only two pieces of each type. One could always artificially make the Diagram use two different Chariot Soldiers and Tetrarchs, each present as a pair. After all, we already artificially distinguish a Lion Hawk obtained through promotion from a primordial one, just to maintain a homogeneous mapping from piece to promoted form.

With the aid of this you would only have to look for enemy Tetrarchs in 4 locations, rather than 256. You would do that in BadZone() when you find 'nodes' increased, and for every Tetrarch you find this way you would set the square surrounding it to 'nodes' on an auxiliary board. Moves starting from a thus marked square would then be suppressed, as that piece would be frozen.