Mel's core ability, her projectile reflection (W), neutralizes many champions' skills, causing extreme frustration alongside her fast and powerful Q.
Her long range, low difficulty, dominant laning, and execution ability leading to kill steals are major reasons for her high ban rate.
Facing Mel with champions like Viktor, who have long range and unreflectable skills, is effective; try to dodge her Q with predictive movement.
Stats
Sorcery + Precision
Q
W
E
R