From Bulbapedia, the community-driven Pokémon encyclopedia.
Dr. Mason's Lab (left)
Deck machine room (right)
The Mason Laboratory (Japanese: オーヤマ研究所 Ōyama Institute) is a location in TCG Island.
When the player goes there for the first time, he or she has to beat Tech Sam's introduction battle, so Dr. Mason can give he or she a choice of three decks to start off with. They are the Charmander & Friends Deck, Squirtle & Friends Deck, and Bulbasaur & Friends Deck. He also gives the player 30 additional cards, which are decided by which deck the player picked.
In Pokémon Card GB2: Here Comes Team GR!, he gives the player his or her first deck, which is always the same.
After getting his or her Starter Deck, the player can get Energy cards by beating either Tech Sam or Tech Aaron. Additionally, after the player gets at least one Medal, they can use the Pre-Deck Machines, which they can use to copy the Clubs' decks as long as they have the necessary cards and the right Medal (e.g. the player needs the Water Medal to access the Water Club's decks).
In both games, after beating the game, Dr. Mason builds a Challenge Machine for card duels.
These are three starter decks in Pokémon Trading Card Game, all of which feature the Kanto starters.