Complex sentence: Enraged by the deception, Fionna takes out the crystal sword to fight, but the sword is another one of Ice Queen's tricks and turns into a ball of ice around Fionna's hands.
Split into simpler sentences: Enraged by the deception, Fionna takes out the crystal sword to fight. The sword turns out to be another one of Ice Queen's tricks and turns into a ball of ice around Fionna's hands.