Driller Cards (ドリラーカード Dorirā Kādo) are cards containing information about things in the Mr. Driller universe. They are similar to trophies from Super Smash Bros.
Driller Cards were first introduced in the GBA port of Mr. Driller 2. You collect Driller Cards by completing achievements given to you. Once you complete that achievement, you will unlock that card. In Mr. Driller Ace: The Wonderful Pacteria, they are called Pacteria Cards. You unlock Pacteria Cards as you use Mewstones on your Pacteria.
Driller Cards represent various characters, items, and other elements from the many games released by Namco. They range from well-known to obscure, even some that were released in Japan only (or have not even been released yet). Collecting them is optional, and do not affect the gameplay of the other modes.
In the GBA version, Driller Cards can be accessed in the Options menu. From here, you can view collected Driller Card, or complete achievements given to unlock that particular card.
In Mr. Driller Ace: The Wonderful Pacteria Edit
The Driller Cards are much different though. Instead, they are called Pacteria Cards. You unlock them as you use Mewstones.
In Mr. Driller Drill Land Edit
There are a lot of Driller Cards in Drill Land. There are a lot of achievements and are split into Gold, Silver, and Bronze.