Plague Before Mashiah Sources

Note: some of the links below use Otzar HaHochma, which is fully open to the public for free for a limited time.  So, I'm taking advantage while it's available - although these links may not work long-term.

1. Dever close to Mashiah
   
   Sources
   Shir Hashirim Rabba (Hazit) 2:29
   Yalkut Shimoni Shir Hashirim 586
   
   
   
2. Mabul of Dever
   
   Sources
   Tosefta Ta'anit 2:11
   Yalkut Shimoni Bereishit 61
   
   
   
3. Gog Umagog as a plague brought about by Hashem against the nations - not as a war fought by the Jewish people
   
   1. Yehezkel 38:22:

      כב  וְנִשְׁפַּטְתִּי אִתּוֹ, בְּדֶבֶר וּבְדָם; וְגֶשֶׁם שׁוֹטֵף וְאַבְנֵי אֶלְגָּבִישׁ אֵשׁ וְגָפְרִית, אַמְטִיר עָלָיו וְעַל-אֲגַפָּיו, וְעַל-עַמִּים רַבִּים, אֲשֶׁר אִתּוֹ.

      22 And I will plead against him with pestilence and with blood; and I will cause to rain upon him, and upon his bands, and upon the many peoples that are with him, an overflowing shower, and great hailstones, fire, and brimstone.

   2. Zecharia 14:12:
      

      יב  וְזֹאת תִּהְיֶה הַמַּגֵּפָה, אֲשֶׁר יִגֹּף יְהוָה אֶת-כָּל-הָעַמִּים, אֲשֶׁר צָבְאוּ, עַל-יְרוּשָׁלִָם; הָמֵק בְּשָׂרוֹ, וְהוּא עֹמֵד עַל-רַגְלָיו, וְעֵינָיו תִּמַּקְנָה בְחֹרֵיהֶן, וּלְשׁוֹנוֹ תִּמַּק בְּפִיהֶם.

      12 And this shall be the plague wherewith the LORD will smite all the peoples that have warred against Jerusalem: their flesh shall consume away while they stand upon their feet, and their eyes shall consume away in their sockets, and their tongue shall consume away in their mouth.

   3. The Netziv on the Sifri (Beha'alotecha 18), in explaining why the Gog Umagog War is called a war when it is not designated as such in Yehezkel, but rather it is designated as a great plague, explains why the Sifri needs to bring down a verse in Zecharia since only there is it designated as a war (fought by Hashem).  
   4. Rav Moshe Feinstein ZT"L in Igrot Moshe O"H vol. 4 siman 81 says that Gog Umagog will not be fought by Jews with any weapons, but rather by Hashem by using the methods mentioned in the verse above in Yehezkel.  (See also Malbim on Yehezkel 39:9.)