On using poison cloud units...

[Vynd]

When I have played around with Pythium Serpent Cult I found that grouping the little hydras with the big hydras was pretty effective, both in terms of damage dealing and also keeping morale up and the troops in action. As others have pointed out its not as if the hydras have bad morale to begin with, it's actually quite good.

People have mentioned that you can add to this army using undead, and potentially archers. I'll add vinemen to the mix. Get some Vine Crowns going and you can churn out a lot of these suckers, and later on, vine ogres. They're both completely immune to poison, and their cost in gems is low enough that you can afford to make a modest amount every turn while still stock-piling gems for bigger and better things. If you're really overflowing with gems and you want a little more punch than vinemen, Horned Serpents are a low-end summon with poison resistance, albeit a somewhat pricey one for what you get.

As for commanders, I thought that the top-end Pythium mage-priests were 100 percent poison resistant. But even if they're only 50 percent, have them, or the cheaper Pythium mage-priests if you prefer, start a fair distance away from the hydras and script them to cast poison resistance first thing. Or make some poison resistance items for them. Either should keep them safe.

So right from the start, if you're willing to spend some gems, I think you should be able to start building an army based around a few big hydras, a lot of little hydras, and as many vinemen as you feel are necessary. It's hardly a perfect army, but it should be highly serviceable early in the game, which is what you're asking about right? As time wears on and you get more gems, and better magic, you can start adding in undead, powerful constructs, etc. And you'll get poison resistance spells that you can use to help you bring more conventional troops into play.