You have spent years running. Training. Getting faster. So fast that you now move inconceivably fast. So fast, you appear as only a streak.

Man of speed

3rd level Way of the Flash feature

Upon picking this subclass, your unarmored movement monk classfeat doubles. 

In addition, once per turn, when you take the dash action and move more than 30 feet, you may spend 2 ki points to make an unarmed strike attack as part of that action and deal additional damage equal to your movement speed divided by 10. This does not count taxabi speed increase, or any other classes speed increase. This does include dash however.

This feature becomes speed /5 at level 17, with the same restrictions as above.

I am speed

6th level Way of the Flash feature

When you take the dash action, you may spend a ki point to gain an additional 20 feet. You may spend more ki points, with every addition point spent increasing the speed by 10 per ki point.

Yummy speed

11th level Way of the Flash feature.

When you hit a creature with an unarmed strike, you may spend a number of ki points up to your wisdom modifier to steal their speed. For every ki point spent, their movement speed is reduced by 3 and yours is increased by 5. 

In addition, if this feature reduces their current speed to 0, you may spend an additional 2 ki to render them incapacitated until they can move again. This includes switching movement types or being forcefully moved. This does not, however, remove your additional speed when they gain it back.

Speed mirage

17th level Way of the Flash feature

You may, once per turn and as an action, spend a number of ki points to a maximum of 3 to create speed mirages each within 10 feet of you. Each speed mirage adds 1 to your ac, as it makes you hard to hit. Additionally, attacks against you are at disadvantage. When an opponent hits you while you have a speed mirage active, you may roll a d20. If the number rolled is 13 or greater, a speed mirage ends and you instead take 0 damage, and any additional effects are not triggered.

In addition, you may spend 3 ki as an action to be under the effects of haste for 1 minute. Being under the effect of the spell this way removes the lethargy feature, but you cannot attack as any part of the hasted action.