The hand
Thirteen orphans consists of one of each of the thirteen terminal and honour tiles — the 1 and 9 of each suit, the four winds and the three dragons — plus a duplicate of any one of them. It ignores the usual four sets and a pair.
When to try
The hand becomes realistic only when your starting tiles already contain nine or more different terminals and honours. It is often pursued from very disjointed hands that have no other prospects.
The thirteen-sided wait
If you hold all thirteen different tiles, you are waiting on any of them — a thirteen-sided wait. Some riichi rules count this as a double yakuman.
Defending against it
When an opponent discards only simples and keeps terminals and honours, be careful with the last copies of terminals and honours late in the hand.
