Personally, early in the game, I go for cards that will help me complete decks , while later I might save up more for getting those big, rare cards
Face-down Pendulum Monsters in the Extra Deck cannot be Pendulum Summoned, but can be Fusion, Synchro or Xyz Summoned (depending on their monster card type)
C Common Scareclaw Belone X EARTH Level 3 [ BeastEffect ] ATK 0 DEF 1700 You can Special Summon this card (from your hand) to your Main Monster Zone, adjacent to a "Scareclaw" monster you control or in its column
Your opponent would want to remove the Mufasa as soon as possible, but now when they do you get 2 free lore
Side Deck 13 UFOroid X LIGHT Level 6 [ Machine / Effect ] ATK 1200 DEF 1200 When this card is destroyed by battle and sent to the Graveyard, you can Special Summon 1 Machine-Type monster with 1500 or less ATK from your Deck in face-up Attack Position