Q: I play "Change of Heart", you then play "Mystical Space Typhoon". Does "Mystical Space Typhoon" destroy or negate the action of "Change of Heart"?
A: It destroys 1 Magic or Trap Card, but it cannot negate the effect of a Magic or Trap Card.
So it is better for you not to use this card against "Change of Heart", "Raigeki", "Dark Hole", etc. It is useful to destroy Continuous or Equip Magic or Continuous Trap Card. Also it is useful to destroy Set Magic or Trap Cards (like a Set "Mirror Force" before you attack)