You can only keep one to mitigate the life loss but that's what makes Sylvan Library so good: you have options and the ability to choose
For Marvel Super Heroes , WotC name dropped Scarlet Witch, Human Torch, Doctor Doom, Squirrel Girl, and Luck the Pizza Dog among many others to make Earth's mightiest, most legends matter set ever
add 1 Pendulum Monster from your Main Deck to your hand." "If this card is Special Summoned from your GY: You can add up to 2 face-up Pendulum Monsters from your Extra Deck to your hand." Related: Pendulum Monsters/Pendulum Zone/Pendulum Scale/Pendulum Summon/Pendulum Effect [spoiler=Pendulum Scale] The Pendulum Scale is 2 numbers on Pendulum Monsters that determine the Levels you're allowed to Pendulum Summon
When you swing you draw and discard, so you get a free loot in any color, on curve, and powerfully
At high-power tables and cEDH, these cards are considered fair game and even necessary to keep fast combo decks in check