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For certain strategies, Chaos is essential for an Elf.
1. As mentioned here, there's the strategy with the Enchanted Ballista. I don't like it because the Ballista is easily destroyed, and it pushes the hero back when it fires. Also, it's difficult to implement due to the low chance of getting Attack and Mechanics skills for the Elf.
For this build, it's important to develop Education with Mana Attraction. Then, there will be enough mana...
2. Chaos works well with developing Rain of Arrows, Enchanted Arrow, and maximizing the number of Cursed Enemies. But Darkness and Summoning also work well here, especially with enchanting area-of-effect spells like Mass Destructive Ray or Fire Trap. I like this option more because it's easier to obtain and harder to counter. And you don't need to develop as many skills.
3. There's a spell in Chaos called Armageddon. There's a skill in Chaos called Fire Lord. And the Elf has a skill in Light called Fire Protection.
The Elf also has Minor Spell. All of this together is perfect for the tactic of burning away the armor of all enemy troops, while the damage to your own troops will be very small, and Armageddon won't burn away the armor of your own troops. At the same time, the hero will receive Storm Wind, Mass Haste, and Mass Retribution.
The tactic in battle is simple: cast Mass Retribution, then cast Mass Haste, and then, each turn, cast Armageddon.
After this, the damage of the Elf's troops will become simply enormous, and the initiative will be increased.
I like this Chaos option the most :)