Any cards that Create lots of Tokens at a time can be extremely deadly for your opponents
Depending on how strict certain events may be, matte or dual matte are generally a safe choice while glossier sleeves may be better suited for casual play or even play-testing
Some of your cards may even have significant value or will continue to grow in value, depending on what cards you collect and how you store them

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It can be used to cast powerful restricted spells multiple times, give a second life to a creature which has been killed, and even be used to return lands from the graveyard to help mana fix
Sylvan Library (green, 2 mana): Three cards per turn, with a life-payment trade-off