On your way to streams of hades, you will conveniently unlock the bog beast. In CBM you get 3 of them for 3 nature gems and it's castable by your capricorns. Now there's something to supercharge your foul vapor strategy
Hear your opponent cry in agony as he succumbs to bog beast fumes protected by waves of skeletons.
Quagmire sounds like a goto spell too, to slow down fast units.
Don't forget that Dragon master is doable now that you keep your nature magic on land. You can make quite a drake factory with ice drakes, earth drakes and wyverns. The wyverns are poison immune and can fly in the rear and paralyze mages, and why not throw in a couple Amphiteres (with girdle and lycan ammy?) as well to further empower your poison angle?