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You can manage & track your card collection and decks once you create an account and login.

Is Plan mandatory? For example: on Secret Dealings it says draw a card, then Plan 1. Are you required to put a card on top of your deck or is it optional?

It says You may, so it is optional.
Source: Wizards of the Coast (2019-02-22)    【Link to Ruling】
Tags: Plan