The card States "If you are the defender and have a Goliath in the battle, your opponent must destroy one of his participating flying units"

What its means? if i have 2 goliath my oponnent have to destroy 2 flying units? and 3 for 3? or always be only one flying unit destroyed no matter how many goliaths is in the area?

Only 1 unit, the number of Goliaths doesn't matter.

Does this ability count as a "Start of battle ability"?

EeT-MeeL said:

Yes, it does. It even contains that text.