InOn Tuchanka in Mass Effect 3, a thresher maw can take down a Reaper. Thresher Maws can be killed by a we get to see
a thresher maw take down a Reaper
In Mass Effect 2 your small unit of highly trained/skilled soldierssquad is able to defeat one during a quest.
If the thing that takes down a reaper can be killed why is a reaperare the Reapers causing the galaxy so much distress and are seemingly so invulnerable?