Eezo

Crassus had a plan. Crassus had a crazy plan
From what he could tell from the Asari biology, there were some form of nodules throughout the nervous system. These were presumably caused by this 'Eezo'... god he hated that term. These Nodules were essentially benign cancerous cells, which explained Eezo causing cancer. If the cancerous cells were benign then the individual would have these nodules, and given their location on the nervous system, they could be stimulated. In the Asari they were all synchronised in their usage, which meant they could produce these fields. Given the natural nervous system of the Asari, which was vastly different to the other species in both the collective and the Equiis pact, it would seem the others wouldn't achieve this... so he needed to sunchronise them...

New Units

Habitat Walker:
The towering Habitat Walker has four long, but bulky legs that it uses for movement and sports dozens of plasma cannons and hardlight turrets. It also has two massive warp cannons and sports a sort of low powered energy projector on it's main body. The walker contains many sophisticated teleporation systems, hallways, storage bays for synths and mechs, which are beamed down through it's teleporation system. The Walker's upper body is somewhat shaped like a lopsided hexagon.
The sheer size of the Walker allows it to destroy many buildings by simply stepping on them with its legs. The walker is also truly "all terrain", able to climb cliffs and mountains or wade through lakes and even be fully submerged. It's external armour is extremely thick, battle ship grade with shielding, making it hard to destroy with most grond based weapon. Rather, enemies should destroy its hardpoints to expose the walker's internal workings, then break the dark energy cores protective casing and from there destabalise the dark energy core through damage.

Assembly Walker:
Like the Habitat Walker, the Assembly Walker is a massive, quadrupedal walker armed with plasma cannons and a teleportion system. It is more than twice the size of the habitat walker, making it a gargantuan walker. The Walker's upper body features two large 'arms' that are covered in weaponry on either side of the main body and a giant teleport device on its back. The assembly walker has hundreds of plasma cannons and hardlight turrets. It sports four massive warp cannons on each arm, and has a newly designed armament, the Dark Engery Caster on it's main body. The Assembly walker acts as a sort of walking manufactorum, producing synths and mechs as it advances across the world, through supplies that are teleported to it en mass
Like the other large walkers, the Assembly Walker can crush almost anything in its path and traverse nearly any terrain, including cliffs. The sheer size of the Walker allows it to destroy many buildings by simply stepping on them with its legs. The walker is also truly "all terrain", able to climb cliffs and mountains or wade through lakes and even be fully submerged. It's external armour is extremely thick, even stronger than that of the habitat walker. Enemies should destroy its hardpoints to expose the walker's internal workings, and from there disable it's internal energy shielding, followed by it's internal protective casing then the dark energy core can be destabalised, causing a self destruction

Reaper Drones

The Reaper Drone is a mech that is essentially a mobile teleporter for breaking down materials (organic or not) and teleporting them to supply ships or assembly walkers. Each Reaper Drone possesses advanced artificial intelligence that allows it to distinguish between different materials and collect them in a prioritised order based on how easy they are to break down, how much of each resource is required etc. The Reaper Drone's teleporation beam works by breaking down an object and teleporting it away over short distances. They have a Heavy Plasma Machine Gun to help defend them, but often they simply use their beam to break down and teleport any enemies who attempt to attack them.