Goblin Matron

When this creature enters, you may search your library for a Goblin card, reveal that card, put it into your hand, then shuffle.

The List

Secret Lair Drop

Dominaria Remastered

When Goblin Matron enters the battlefield, you may search your library for a Goblin card, reveal that card, put it into your hand, then shuffle.

Because the “search” requires you to find a card with certain characteristics, you don't have to find the card if you don't want to.

If an effect refers to a “[subtype] spell” or “[subtype] card,” it refers only to a spell or card that has that subtype. For example, Goblin War Party is a card that references and creates Goblins, but it isn't a Goblin card.