RULES UPDATE: "this only affects Tribute Summons..."

After many months of investigation we've reached a roadblock... there's no evidence that Konami's rulings change [1] regarding "Rivalry of Warlords" and "Gozen Match" took effect at or before SJC Edison. Thus the responsible and prudent course of action is to apply the Upper Deck Entertainment rulings [2] to the cards. This change only affects the ability to Tribute Summon (not Special Summon).

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 Moving forward, apply these UDE rulings to Rivalry and Gozen: 

• If you have only 1 monster on the field face-up, you may Tribute it for a monster that is a different Type/Attribute.
  
• If you have 2 monsters on the field face-up of the same Type/Attribute, you cannot Tribute 1 of them for another monster that is a different Type/Attribute (even "Jinzo") as you would then have 2 different Types/Attributes.