+1 to proximity mines
As this game if movement based an item to disrupt flow would be a new aspect. A snare to trap a mech to a limited area, change the disrupter to invert your controls, or an item that pushes mechs away
On movement how about thrusters that push your mech down as a way to end a jump earlier or eliminate the set trajectory from jump pads
We have a heat charge to help incin & harm others. Why not the inverse & a cooling charge? Allows a team to better hunker & defend a point my mitigating heat
Impact damage. If we have 'crushing damage' why not from a body slam or crash
Mines are skilless, free damage. I'd rather see a detonating charge. Something that you actually have to pay attention too. That would also allow the item to do non-trivial damage, yet be balanced.
As far as snares, knockbacks, and the like, those are generally mechanics that are avoided in games because they are anti-fun. Sure, if you're using them it might be nice, but for most people, when they are hit by something that removes control from them it's nothing more than frustrating. There's a fair amount of research about this sort of thing. Riot, for example, looked into this.
Air Compressor.
As if this game isn't already defense oriented enough already. Also heat management is ridiculously easy. There's no need for such an item. If you're having trouble managing heat, it's simply a matter of becoming more skilled at it.