Speedster is easily the most abusive character concept. High offensive and defensive CV's, lots of movement, lots of damage dealing, good justification for being difficult to detect or damage, and of course, high SPD.
Move by's with high OCV can be especially problematic, as speedsters can quite often do Multiple Move by's on the same or different targets, knock them down and then run completely out of sight around the corner of the building. If the speedsters damage classes aren't capped well below everyone elses the other team members will just be mopping up after speedy boi zooms in and knocks everyone down and then runs out of harms way, only to do it again before the other characters even move.
Probably the single greatest sfx description I ever heard came from a speedster player. 'Can I run up to him and hit him?' 'Sure, he's in sight' 'I'll fire my PD Energy Blast at him. The sfx is I run up and hit him and then run right back here so fast he can't react' '........'