As long as this unit is in the Ground arena, each of your other Ground units gets Critical Hit 1 (While attacking, this unit does 1 more damage if you roll at least one natural six. No matter how many dice come up as 6_s, the unit still does only 1 more damage. A 'natural' six is one where one of the dice actually shows a six, before any bonuses or penalties. Critical Hit is cumulative).