Originally Posted by Ismashthings7x22
There is nothing in the rule which says you don't get tough if you are already knocked down. You would follow the rule exactly as written until you get to the 'is knocked down' part, at which point, being already knocked down, the attack is resolved. You can't be knocked down again, but you continue being knocked down from the first tough check.
Destroyer of Worlds
Think of advantages, such as tough, as always active.
The only time you do not get use of such advantages, is if another model's spell or ability states that you do not gain the benefit of your advantage.
For example, MacBain!! has the special rule of Grievous Wounds on his melee weapon, which does not allow healing or tough checks.. If he were to box a model with the Tough advantage - say the Trollkin Champion Hero, the Hero would not get his tough check.