bold harness
The Kai's reap ability isn't very affective. It has limited uses because you can no longer choose which unit to reap, and it can even cause problems when used poorly.
So what if the units it reaps becomes more vulnerable and they take more damage from attacks until the effect is gone, the effect could even stay for a short while after the target stops being dragged behind your army. You make your target vulnerable while your army does the damage, unlike SW2 where the reap is the one doing the damage. The reap ability is good for stopping retreating units and this could help make sure the targets won't survive.
Maybe they take 5% - 10% more damage?
torpid wraith