With a touch, you cause your familiar to double in size, becoming a fierce guardian creature. This increase in size doubles the familiar Hit Dice, increasing its attack bonus and saving throws accordingly. The familiar's size increases by one category. This reduces its Armor Class, reduces its attack bonus, and affects its ability to grapple, but grants it an enlargement bonus to Strength and Constitution and an increase in the damage of its natural attacks. The familiar retains all of its special abilities.
When the spell ends, your familiar returns to its normal size and all damage it took while empowered is reduced by half.