Use a few Barrier pieces with Construct... and/or Icicle or Toro (i think)with Construct. You can wrap up Flash and stop him in his tracks (he will have a breakaway roll if you don't seal him on all sides)... and with Icy/Hot do some damage.

Construct 14 points
Sets:Green Lantern Corps
Prerequisite: Barrier
Choose a character. Any opposing character adjacent to a barrier marker placed by the character that attempts to move (or would be moved by a power, ability, or effect possessed by another character) must attempt to break away. The effect of this feat ignores powers, abilities, and effects that allow a character to break away automatically.

Now that I think of it... can you use Construct with those 2?

Either way... Construct on Shaman is one of my favorite opponent's combos.

mmmmmmmmmmmmmm combos

Toro's Firewall is a good option also as it does not require an attack roll. The downside is that the Special Power is a late dial occurance.

Nope. Special Powers won't work unless they have Barrier showing at the same time as their special power. Which I don't believe is the case.

Some of the best tactics have already been named. You need damage that doesn't rely on attack rolls.

That means Icicle, LAMPS (or PADS :P), Mystics/Wildcards and I would add: Arcade. Arcade with Twart could realy mess up with KC Flash, especialy one with Nanobots.