Speed

Speed is a status effect which increases an entity's walking speed by 20% multiplied by the effect level. It expands a player's field of view (FOV) accordingly. Negative levels will decrease speed.

Unaffected mobs
Flying mobs are unaffected by the Speed effect.

Trivia

 * Speed allows slimes to jump farther. High levels of speed can make slimes bounce out of view with just one jump.