Boon of Thunderous Speed (5e Epic Boon)
From D&D Wiki
Boon of Thunderous Speed
Your body is charged with energy when you move, so much so your very passing can cause shockwaves to be produced.
- Your walking speed is increased by 10.
- If you move at least 100 ft. without moving through the same space twice on your turn, all creatures you pass within 10 feet of must make a DC 15 Strength saving throw or take 2d6 thunder damage and are knocked back 5 feet. On a successful save, they take half damage and no additional effect.