Why did Moshe use the title "Elokei ha'Ruchos"?
Rashi: Assuming (mistakenly) that Hashem was about to destroy all of Yisrael, Moshe pointed out that if, following a rebellion, kings, unable to distinguish between those who sinned and those who didn't, punish them all, Hashem certainly can. 1
What did Moshe set out to achieve with his Tefilah?
Rashi and Ramban #1 (citing R. Chananel): He Davened that Hashem should change His mind and punish only Korach, Dasan and Aviram. 1
Ramban #2 and Targum Yonasan: He set out to remove the punishment from the people 2 and to place it fairly and squarely on the shoulders of Korach and his henchmen, who were directly responsible for the rebellion, as is the way of those who plead for mercy on behalf of the masses. 3