In a given game, you only see so many cards. Most games, a player is likely to see their starting seven, their first card drawn, and their card each turn for roughly eight turns. In a medium-to-long game, you might see 15 cards, or 15% of your deck. If you have 10 copies of a card or effect, you’ll likely see one, maybe two in a game. If it’s something you really need to see, like a win con, you want to increase the amount of cards you see. This can be done any of a few different ways:
These cards increase the amount of cards you see over the course of the game, but not the amount of cards you have an opportunity to use. As a result, you can pick the cards you want, but are still reliant on your draw step to gain access to them.
Scrying-
Scrying increases the amount of cards you see, but not what you have access to. It lets you look at the top X cards of the library, then put them on top or bottom in any order. Cards like Augury Owl help to set up the next turn or turns, but things can change between now and then, and you don’t get immediate access without help. Thankfully, many cards that Scry, like Preordain, are also cantrips! Shuffle effects also help to recycle cards that were bottomed earlier.
Self-Mill-
Like Scrying, Self-Mill, by itself, doesn’t provide access to the cards that are binned. Self-Mill is when you put cards from the top of your library directly into the graveyard, such as with Stitcher's Supplier or Dredge. Surveil is a somewhat similar mechanic, which is kind of the sweet spot between Scrying and Self-Mill. Self-Mill works best when the cards themselves can be cast from the grave, like Flashback or Retrace, if you have a reliable way to access the cards, or if you care about the amount of things in your grave, like Rielle, the Everwise.
Exile-
Recently, Red has received a lot of cards that exile the top X cards of the library, and then provide temporary access to them. This prioritizes the exiled cards over the cards in your hand, which can be either card advantage or disadvantage depending on how easy the cards are to use. Cards like Light up the Stage use minimal mana and enable multiple spells to be cast in a turn, fueling Prowess and Magecraft.