Damage those monsters deal in excess of the total defense of their blockers is dealt to your opponent.
Based on the wording, he doesn't do damage above EACH character, but instead the total defense versus the damage he deals. This will nearly always be the same thing.
In your example, he deals 27 damage, but the Sidekicks have 3 defense (total). He deals 24 damage to your opponent.
If Doctor Octopus was blocked by 3 characters, one with 20 defense, and two each with 1 defense, he'd deal 5 damage to your opponent (27-22=5).
-The Dice Masters Rules Team