X-Men: Evolution (2000)- Season 4, Ep. 7
"Ghost of A Chance": A young mutant named Danielle Moonstar saves Kitty from danger and Kitty gets her to join the Institute. Soon Danielle's presence at the school causes the other students to have powerful nightmares. When Danielle disappears, nobody at the school seems to remember her except for Kitty, who still receives messages from the strange girl.