In sanctioned matches at events that are either Competitive (Comp) or Professional (Pro) rules enforcement level, your deck must be match the contents on the deck list that you submitted at the start of the event. This applies to both constructed and limited events.

Many limited Regular (Reg) rules enforcement events do not require deck lists and also allow players to change their decks in-between matches. In other words you can change what is in your deck for the first game of the match as long as you are still only using those cards that are in the pool of cards that you received. This is sometimes referred to as ‘continuous build’ as you are allowed to continuously change your deck.

If you have any questions about what the rules enforcement level of an event is or if you are unsure if an event allows you to continuously build, ask a staff member of that event.