What You think about new very strong emiters in random place on field, showing after destroy all base emitters. How strong emiters might be calculated on base my reactor/techs and other...
In CODE mission the next difficulty marked as extreme. And much harder moving enemy if no in surface.
Something harder, because if is no surface enemy, every mission is like: very easy

And something extra, like Thor, can will be build very long time. So, this thor can be enemy as well, constructed by enemy creeper

Can be destroy only with experimental weapon.
And upgradable reactors

And bigger maps, please...