Conjuration? Black Servants in trinket armour!
Seriously, conjuration may be only secondary target, but never forget to go to Earth Power - else you'll be wasting a hell of a lot of earth gems for bigger spells like Earth Grip or Destruction. Magma Bolts can be done unaugmented, though.
And, water-blessed giants? I'd wager you're more probably seeing earth/nature bless, but in any case, anything that can be swarmed by size 2 units isn't probably going to rely on defence for too long.