Haste

3rd-Level Transmutation
Casting Time: 1 action
Range: 30 feet
Components: VSM (a shaving of licorice root)
Duration: (C) 1 minute

Target. One willing creature that you can see within range.

Effect. Until the spell ends, the target's speed is doubled, attacks against it are made with Disengage, it has Advantage on Dexterity saving throws, and it gains an additional Action on each of its turns. That action can be used only to take the Attack (one weapon attack only), Dash, Disengage, Hide, or Use an Object action.

Special. When the spell ends, the target is dazed until after its next turn, as a wave of lethargy sweeps over it. If a creature is ever under the effects of the Haste and Slow spell simultaneously, both spells end immediately with no drawbacks.

At Higher Levels. When you cast this spell using a spell slot of 5th level or higher, you may target one additional creature for every two slot levels above 3rd.

Source: PHB 250, SRD

Changelog

Added upcasting option.
Changed crash effect to be the Dazed condition.
Changed AC boost to disadvantage on incoming attacks.
Added caveat about Haste and Slow canceling eachother out.