6 Holo, reverse holo, or non-holo A holo (shiny artwork) is almost always worth more than the non-holo version of the same card
Mendicant Core, Guidelight Look up and down this ranking and you have some amazing options worth copying once you get up to speed
Unfortunately (or fortunately, depending on what you think of remastered sets), most of this list comprises classic cards that are just worth looking out for
You may put any number of them into your hand and the rest into your graveyard
These cards are generally not expensive, but when a card is used often in competitive play, it can be sold for around 1,000 JPY (~US$6.74) per copy
Pair it with tokens like Food, Clues, or Treasures, and it turns into a steady stream of card filtering that keeps your deck running seamlessly