Rule 806.4.b
If the chain item does not fulfill the conditions by the time step 5: check legality has been reached, the actions taken while playing it are undone and it is returned to the zone it was played from if it is a card.
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If the chain item does not fulfill the conditions by the time step 5: check legality has been reached, the actions taken while playing it are undone and it is returned to the zone it was played from if it is a card.