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I have an idea for a composite artifact... the collection consists of: a book of water magic, a sphere of torrential rain, and a charm of negativity (in the form of lightning, I just don't remember the exact name). This collection grants the bonuses of all its components, plus each turn in battle, the hero casts the "lightning strike" spell on a random enemy unit (50% chance of casting the spell) at their own mana cost, without losing the ability to cast other spells.
The name of the collection is "Storm Charm."
Appearance: the same as the charm of negativity, but instead of one lightning bolt, there are several.
I just think the bonuses might be a bit too strong.
Added 12 minutes later:
I also came up with a 5th-level spell. It's called "Geysers" (water magic). The spell creates geysers on the battlefield (the number increases with the hero's water magic skill). If an enemy unit is on a geyser, it "awakens" and starts to act. It deals damage to the unit and pushes it back several squares, and the unit loses its turn if it was supposed to move further.