Steven Universe - Gotta Get Back To The Past

Long ago on a planet Earth, I, Pink Diamond, the shapeshifting master of gems, unleashed an unspeakable evil. But, a foolish rebel warrior wielding a magic sword stepped forth to opposed me. After the final blow was struck, she used her tears to revive me and turned me into a lion. Now, the fool seeks a way to protect her friends and save her planet from wrath of other diamonds

You can't use the portal when the enemies are nearby.