After your total ATK has been figured, and the target's armor and VIT defense have both been factored out, the game then looks at size/race/element/special percentile boosters. TG counts as either size or special (can't remember which it is here), but the equation works like this:
Damage * (1 + size %) * (1 + race %) * (1 + element %) * (1 + special %)
Let's say after figuring total ATK - target's (assume demi-human for this case) armor and VIT defenses, you are looking at a damage total of 200, and let's assume TG is a special card.
With 1 TG: 200 * (1 + 0) * (1 + 0) * (1 + 0) * (1 + 0.2) = 240
With 2 TG: 200 * (1 + 0) * (1 + 0) * (1 + 0) * (1 + 0.4) = 280
With 3 TG: 200 * (1 + 0) * (1 + 0) * (1 + 0) * (1 + 0.6) = 320
With 2 TG and 1 Hydra: 200 * (1 + 0) * (1 + 0.2) * (1 + 0) * (1 + 0.4) = 336
Now, that still may not be the final damage. After the game calculates the above bonuses, it then calculates size/race/element/special damage reductions that the target might have (Deviling, Toad, etc).