Which type of tournament allows players to modify their main deck from a selected pool of cards before games?

The type of tournament that allows players to modify their main deck from a selected pool of cards before games is typically a Limited tournament. In this format, players are given a limited number of cards to build their decks. This usually involves a set number of booster packs from which they can select cards to create their decks.

In Limited formats, players construct their decks after seeing the cards available to them, using only the cards they have opened or been given. This can involve using cards from a single pool for a specific event, allowing for more flexibility compared to other formats where decks must remain the same throughout the tournament.

While Constructed tournaments require players to build their decks in advance using a pre-defined card pool (based on legality and formats), the essence of Limited events focuses on building decks during the build phase from a specified gathering of cards. Draft tournaments, while also Limited, involve selecting cards from booster packs in a specific order and do not allow modification once you create your deck. Sealed tournaments allow players to build their decks from opened booster packs while adhering to similar restrictions. Thus, Limited tournaments encompass the concept of modifying decks based on a predetermined pool of cards.