The Speed Force claimed that Barry broke his promise to help it and that it had to kill Alexa now in order to save itself.
Badly beaten and weakened from the race, Hunter could only scream in terror as the Time Wraiths surrounded him and began forcibly transforming him into a demonic-looking skeletal being, changing the lightning-bolt emblem of his costume red as well as its outline and the earpieces as well as turning the emblem circle white and turning his speed lightning red.
Recreating the reaction that gave the Flash his speed resulted in Eobard becoming a speedster and gaining super speed and the power of through a Speed Force connection.