[Wauthan]

You could always run a "Toxic Avenger" game. It's pretty fun since it's a very unusual way to construct your armies. Basicly the whole idea is to do the largest possible amount of poisondamage to your enemy as fast as you can.

Using the Serpent Cult Pythium with a Green Dragon pretender is a good start. Hydras cause immense amount of poisondamage, are immune to poison and are the thoughest sacred units in the game (which really works well since you wanted to focus on a single type of magic). Pythium starts with Summon Horned Serpents and can easily get access to Bog Beasts (also known as toxic artillery). Breath of the dragon lets your theurgs do their part in drowning your enemies in bile while vinemen/ogres serve as the meatshield. When you get access to minor death magic the lesser undead are also an option.

It's pretty easy to make similar elemental focus strategies with fire (firedragon with abyssians, using firedrakes, fireserpents, devils and the likes), lightning (air10 virtue pretender leaning heavily on sacred troops and the few lightning resistant summons) or ice (Blue dragon with Caelum or Jotunheim using undead, icedevils, icedrakes etc) but the choice of troops are more limited.

The Boo! strategy focusing on Death10 blessing and getting as many fearsome troops as possible is pretty funny as well but a lot harder to pull off.