If he's always hiding behind a heavy jack, then see if you
can slam it to knock Kreoss down
Play the game knowing that you're going to be
KD ed at
some point. To totally protect against it, you have to be further
than 12" away from Kreoss, 15" if Kreoss can charge something.
However, one way is to force him to use the feat defensively.
Don't let him use the feat on a turn when his warjacks can
come at your warcaster. Stuff heavy hitters down his throat.
Have shooters lined up to snipe at him (if they stand up, they
shoot him since they sacrifice movement). Trenchers can
put down smoke so that Protectorate forces can't break through
on Kreoss's feat turn. Skorne put up a shieldwalled unit that
will count as being in shield wall even though they are knocked
down that turn. There's a lot of different ways, but those are
a few that have made me lose in the past