Mafia 77. Brave New World

How would "engine explosion" work in this case? The other player might have additional visitors (who came to him directly, not to the firefighter). Would it kill everyone?

No, that would be too much. It kills the firefighter, the other player, and the visitors of the firefighter. If the firefighter is healed, the other player will also be alive, but the firefighter's visitors will not be revived.

Well, it's clear here: the firefighter dies as if he visited the other player. At the same time, everyone who came to the firefighter should remain alive.

Yes.

What's the point of playing then? You could immediately declare "Mortgage" the winner and start a new game.

Indeed. Okay, let's keep it at two. If even a "Heroes" player agrees!
Added the order of Non-Damage effects in the second post. I highlighted different types of Non-Damage effects in different colors; it should be more convenient...