Hey guys, I need your help. If a character with Hypersonic Speed (i.e. Superman) attacks an opposing character that has the Mystics TA, does it take one unavoidable damage right after the attack or can Superman finish his movement and then take the damage?

If someone could help me soon, I would appreciate it.

He would take the damage immediately, and then continue his movement (assuming he still possessed HSS).

Queenie is correct.

Also, if his speed value decreases, his range to move is reduced accordingly. If his speed value increases, he doesn't get any added range, though.