Answer:
a. 1. You would want the regulatory boards to see more competition, so you would argue that the relevant market is all toys, which is as broad as possible. This would make it less likely that the merger would violate merger guidelines.
b. 2. You would want to use the narrowest definition of the market, which would be dolls. This would make it more likely that the merger would violate merger guidelines.
Step-by-step explanation:
a. In order to avoid anti-trust laws, it would be best that Mattel convinces the authorities that the relevant category is all toys not just a subsection. This will show that the toys made by the new company would have a lot of competition from other toy makers across the board which would reduce their chances of being a monopoly and violate merger guidelines.
b. As the bid is unsolicited, Hasbro might want to defend against it. In which case their strategy should be the exact opposite of that of Mattel and they should try to convince the regulatory boards that they would be in the narrowest of markets which would be dolls. This would mean that the merger has a strong chance of leading to a monopoly and would violate merger guidelines.