Answer:
The underlined dependent clause in the sentence is that comes with a gift certificate, and it functions as an adjectival clause.
Explanation:
A dependent clause is a clause that cannot stand on its own, it needs to be part of a bigger sentence. In this case, you cannot just say 'That comes with a gift certificate.' because something is missing.
Also, since that clause is describing the noun trophy, it's an adjectival clause because adjectives closely describe nouns. What kind of a trophy? A trophy that comes with a gift certificate.