Complex sentence: Each card can be leveled up and has a star rating--the level cap; the player can sacrifice a card to level up other and, by fusing two equal cards, the player can increase a card's level cap.
Split into simpler sentences: Each card can be leveled up and has a star rating--the level cap--players can sacrifice a card to level-up. By fusing two equal cards, players can increase a card's level cap.