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

Since I'm not privy to what happens between two fictional characters in a hypothetical situation, do I just choose who the Mini-Cassette goes under which deployer?

Yes, you choose.
Source: Wizards of the Coast (2019-08-09)    【Link to Ruling】
Tags: Blaster, Communications, Blaster, Communications, Soundwave, Communications, Soundwave, Communications