parshanut torah comment - Could the destroyer in Egypt discriminate?

In Rashi's comment to Shemos 12:22 we read

ואתם לא תצאו וגו': מגיד שמאחר שנתנה רשות למשחית לחבל אינו מבחין בין צדיק לרשע
…once permission has been given to the משחית (destroyer) to damage, it does not distinguish between a righteous and a wicked person.

however earlier in pasuk 13 Rashi cites the mechilta which states

אבל הווה הוא במצרים הרי שהיה מצרי בביתו של ישראל, יכול ימלט, תלמוד לומר ולא יהיה בכם נגף, אבל הווה במצרי שבבתיכם, הרי שהיה ישראל בביתו של מצרי, שומע אני ילקה כמותו, תלמוד לומר ולא יהיה בכם נגף
…Thus, if an Egyptian were in an Israelite's home, you'd suppose he could escape [the plague]; the verse tells us "there won't be a נגף, plague, in you" — but there will be in the Egyptian in your homes. Thus, if an Israelite were in an Egyptian's home, I'd understand he'd be smitten like him; the verse tells us "there won't be a נגף, plague, in you".

1. Are the terms משחית and נגף equivalent? What "force" is doing the killing exactly?


2. Can whatever agency that is performing the killing on that night differentiate between Jew and Egyptian?


3. If it can discriminate, what is the need for the sign of the blood?


4. Why does Rashi in pasuk 22 contrast צדיק and רשע and not Jew/Egyptian?


5. Why is this destructive force able to differentiate between firstborn and non-firstborn of the Egyptians but nothing else?