[Baalz]

I don't know, I think there's actually a pretty decent range of things you can do if you're thinking boosters and gems. Sure you don't have the obvious goto spells some nations have and some nations will be fielding more directly effective mages, but then again you're fielding giant troops with Morrigan support so your mages don't have to be as directly effective. Sure, you're gonna want Kings where you can, but for smaller raiding/skirmish parties a druid or two can be just perfect. They can also take care of support spells for bigger fights leaving the kings free to be SCs or cast the real big spells (darkness, wrathful skies, etc).

A2 - storm power (or gems) & thunderstrike obviously, also they're tough enough to drop mistform then blast orb lightning from among the front line or even lightning resistance and shock wave.

W - with a water bracelet (or W gems) you can drop freezing mist, which is very, very good in combination with undead troops, skellispam, etc. or even just leveraging your much higher hitpoints and regen. Can also drop quickness & quickening which is iffy for your encumb-5 giants, but very, very nice for Morrigans. If you're in the water (which you should be) you can drop shark attack, friendly currents & grip of winter.

D - With a skull staff already mentioned wailing winds & winds of death. Also, terror, shadow blast, disintegrate, and skellispam (which tends to be a good counter to giant-slaying things).

N - healing mists works well with your giants and VBF mentioned fairies. Swarm is a staple spell, and panic stacks well if you're dropping terror with wailing winds along with something having a fear aura....like Morrigans. With a couple bigger boosters you're looking at mass regeneration and relief - both great spells for your giants.