The Behemoth is a Reaper creation,formed from an Elcor. Like Ravagers,Behemoths are artillery units,designed to thin out crowds and pierce defenses. However,instead of twin launchers,a Behemoth has a single large mass accelerator cannon attached to its back that fires off an extremely powerful round that can decimate even heavy vehicles such as a Mako tank. Unlike the species they are created from,Behemoths aren't afraid to get in close to their enemies,raising their upper body to a degree almost never seen in regular Elcor in order to slam their forearms onto the opposition below.
Would've made more sense than the Rachni. Maybe even as a chance for variety; if you killed the Rachni in Mass Effect, the Reapers don't pull something out their asses to resurrect them but are instead forced to use these; bigger, more powerful, but way less mobile and common. If you did, the Elcor are shunted to heavier battlefields, given an in-game buff, and only rarely seen by Shepard him/herself.
Or, since I actually hate the Rachni being used as artillery to begin with, why not have only Elcor artillery and keep the Rachni as a mechanized version of their Mass Effect role; big, kinda fast and terrifying Melee units. Add some reduced health and force them to go into a compacted, less lethal form for tight spaces and they'd be an excellent, if perhaps situational enemy which, again, could be taken out and compensated for if people decided to kill the species off. No Rachni to convert? Not a problem; throw a swarm of husks at the player.
I love the incorporation of the aesthetics from the Ravager and the Scion. Y'all thought they where bad when they had two legs? Now they can run like gorillas and punch through ship hulls! God I wanted to see these things in the game. SOMETHING to do with other races reaper-ized, than just 5 races.
The Heavies are Elcor turned Husks and are the most feared of all the Reaper's ground forces according to the latest Allaince Survay. In battle Heavies act as slow moving tanks and arttilery units, giving covering fire to other ground forces with their mounted guns before moving in and finishing the job. While their main gun is perhapes the most feared part of their arsinel, with a range of over a hundred miles and enough fire power to take down a building, they are also a force to be reconised in close range. For this, Heavies use smaller guns mounted on their wrists, which can switch between full on and semi artimatic as well as their eminse size and streangth. There has been videos of a Heavy ripping a full grown Krogan in two.
Warning to all solders, like Elcor Heavies are much faster than they look and are able to stand on their hind legs when they need to use both of their wrist guns. Do not make the mistake of thing that they are lumbering behamous, they can run almost as fast as a human when on all fours and have much better endurance. When fighting Heavies attack their flanks since they have terrible agility and never face one alone.