A couple of weeks ago the ACT Junior Chess League held it's annual Transfer Tournament. (For those unaware, Transfer is the named used for Bughouse or Tandem Chess in Australia). The difficulty in running this event is that there are some subtle variants of the rules for Transfer, some of which only make sense if you are playing online.
So for information here are the declared variants to the rules that others may use.
Firstly, the reference for the rules we used was http://www.chessvariants.org/multiplayer.dir/tandem.html
The changes from these rules were
You can drop for check, but not for checkmate. Dropping for mate and pressing the clock is considered an illegal move (and the opponents can claim a win).
Pawns cannot be dropped on the 1st or 8th ranks.
There is no promotion. Pawns reaching the 8th rank just sit there until captured.
Partners can offer any sort of advice, even going so far as to suggest actual moves. The however cannot touch the pieces or clock on their partners board.
Castling can only take place with the original (ie non-dropped) rook.
The trickiest (and most controversial) rule is the no-drop-for-mate rule. This rule has been around in Canberra since I started playing chess over 25 years ago, although it's continued existence probably has a lot to do with old hands like myself arguing for it's retention. Indeed when it was announced at this years tournament, it was met with a chorus of boos from the mainly under 14 crowd.
The no-promotion rule is simply to make OTB Transfer easier to handle. No running after spare queens, and then trying to remember if it was the promoted queen or the original queen that was captured (and therefore turned back into a pawn).