Is this specifying which among the highest rarity is discarded? If you explain what it is that this card should be doing, we can work out the text.
Your confusion is more than justified~
The intent is to discard cards which have any effect only in when you have done X a turn before. Cards with effects which come into play only in reaction to what you did. E.g. Runic keyword, Siege keyword, Graceful charity, Guardian spirit, Spring wood, Goblin saboteur, Abyssal scavenger, and further.