Annette, an Ardat-Yakshi, makes a DAMN GOOD attempt EAT ALL OF THE COMPOSITE SOULS OF A REAPER (she manages 10 million). Holy Shit Quotient reached, exceeded, and then exploded.
Chapter 37: during his Trial to become a shaman, Grunt encounters a Thresher Maw. Not only does he get it to back down, he tames it.
Shepard completely destroysMorinth when the latter hits Shepard's Berserk Button. Shepard goes full Avatar State, beats Morinth into a pulp, and then spaces her while declaring her an example of what happens to those who fuck with the Avatar's loved ones. And when we say "Space Her," we mean "Fire her out of Omega at FTL speeds, accidentally throw her into the Omega-4 Relay, which picks up on her Biotic Field and transports her to the Collector Base, where she lives just long enough to see where she is before she asphyxiates." Holy shit.
The attack on Leviathan's hideout. All of it. Special mention goes to: