when dr doom masterminds the damage to grundy does he roll for impervious and get the minus 2 or not.

Yes, Grundy does, because Impervious triggers upon damage received, not targetting (like Super Senses).

It's actually because Impervious activates against damage dealt and MM deals damage.

Super Senses does not require a character to be targeted, but it does require a character to be hit by an attack. (Splash damage for instance is not targeted, but SS works against it.) MM damage is not damage from an attack which is why SS does not activate against it.

Oh, right, I forgot that about Super Senses...thanks for reminding me!