The one with the reactors that have to be infiltrated with engineers nearly simultaneously. The easternmost reactor stops 'accepting' engineers after the first or second infiltration. So I screwed up twice and now I can't complete the mission.

you have to assasinate the emperor with 1 unit i mean wtf how?

Laz0rs everywhere after a while, my co-commander gets raped, the enemy forces hit you with everything they've got and a wing of 4 Century bombers can't take more than a third of the firebase's health bar (if no aircraft are shot down before dropping their payload). I just don't have enough time/resources to do everything I've to do.

each laser has his powerstation, you can easily capture those (dropping a engineer from a plane), they won't recapture them. After its simply a question of opening an entrance (knocking off the defenses) and then enter with a little army of tanks (whatever mix you have) and go to the back of his base, knocking off his resources and power. Then everything crumbles and all is done. Or you can simply use planes to knockoff all his energy buildings first too, but its way faster with a ground force once you can enter.