Basically when you pick up the powerup then when somebody damages you severely or uses a powerup on you then that would happen to them instead.
For some examples:
Getting severely hit will damage the aggressor instead and any knockback will also happen to them. (same applies with the rocket booster)
When getting hit by a boulder the boulder will ricochet off you and move towards the aggressor
When a tornado goes your way it will go towards the person who used the tornado
etc
