Trying to think of some things that are not normally included but might be practical. Harder than it sounds given the limitations of the medium but here goes:
Units that recycle the environment or the enemy casualties (and their own) to produce new units. Borg/Strogg/Total Annihilation style.
Armaments that turn terrain into death traps, like filling buildings with marmite, melting trees, compelling all animal-life in an area (bound to be insects/arachnids around at least) to start attacking all who enter.
Something akin to the the BFG 10k from Quake 2 (shoots an energy ball that attacks every enemy it passes by before exploding on contact with a surface/enemy).
A weapon that acts like giant magnets in old cartoons that can pull and throw their target around.
Hallucinogenic gas was an old fun toy that seems to be forgotten from things these days. Makes enemy units act unpredictably rather than just stuns/pins.
Weaponry that shoots projectiles that follow a programmed path of limited stages (ye olde Blaster bombs of XCOM, possibly the Redeemer of Unreal Tournament; essentially a slow, very finely guided missile) to reach targets that may be known but can’t been seen.
Infantry and other small units that can continuously hover yet are reasonably armoured (XCOM flying powered armours and drone tanks).