[Expulsom] is obtained primarily from scrapping armors and weapons using the Scrap-o-Matic 1000 (Alliance), or the Shred-Master Mk1 (Horde). These tools work like disenchanting, you can break down any gear obtained that is from the Battle for Azeroth expansion, including dungeon/raid drops, quest rewards, world drops and crafted gear. The Scrapper isn't restricted to specific trade skills. Anyone, even people without a crafting skill can use it. You will mostly get ores, gems, leathers, cloths, and occasionaly you will get one [Expulsom].
Mythic+ rewards will also go up by 30 item levels; however, during the first week of Season 2, rewards from end-of-run chests will be capped at Mythic 6 quality (item level 385), and the chest you open next week will contain Season 1 rewards if you do a Mythic+ run this week. (So, for example, if you do a Mythic 10 during the final week of Season 1, you’ll get a Season 1 item level 380 piece and 60 Residuum from your first Season 2 chest.)