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A prime example in Pokemon just came up at a small 8 person, best of the best invitational tournament, where David Cohen allowed Tsuyagashi (or something) Yamato to take back an energy attachment, and lost the game because of it. Should David really be kicking himself for being a nice person? No. That's ridiculous.
but I would force them to take it back and hand it over, not fall away themselves
Why would it be 'wrong' to play SoG/NJ if you're reading a SoG/NJ that will end the game? It was the absolute correct play by the opponent, even if it was a bluff.
If the defender expects the opponent has a Son of God and New Jerusalem that will end the game when they hand over the soul they should play their own Son of God and New Jerusalem before surrendering it.
3 - If you REALLY want an example of dishonorable play, you should check out this thread. At least your problem was a spur-of-the-moment decision made in the heat-of-competition of a game. This other example was premeditated.
Every time one of these dominant scenarios come up I swear I get even more confused on how they work...