Burning/Poison/Cold damage

[Xargon]

Yes, both of those are very useful for the burn/cold effect. The spell blizzard is also extremely powerful. With a bit of int and destroyer 3, a lvl3 blizzard hits for 4k damage and freezes everything. Against enemy heroes who have their troops splitted into 10 stacks or something like that, that battle can be almost over after the first round: cast something, then blizzard, then afterwards lord of the north (so the blizzard won't destroy the shards). This makes even invincible heroes very easy (but will probably change at least a bit later in the game).

[camelotcrusade]

I've been loving poison cloud, especially when you have celestial guards from the royal griffon or loki's touch from soothsayer. The celestial guard is immune to the poison cloud so he can lure enemies into it, and of course with Loki's touch they surround the mob in their midst so you can poison the whole army if you're lucky. For bonus points, have an alchemist toss a poison bomb on the rabid enemy and theh they get hit with poison twice on their turn (since poison cloud seems to be separate).

[Xargon]

But there is no greasy mist for poison
Nearly doubling the burning effect is pretty damn good for a measly 5 mana (especially when the stacks are very large...)