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1. If I'm leveling up an Elven Warrior, I try to maximize the attack and damage of my troops, so I take Battle Balance + Retribution (I always take Leadership because of the speed aura) and Speed Magic (if I'm leveling up a Light hero, I take Archery instead of Speed Magic).
2. If I'm leveling up an Elven Marksman (very rarely), I take Archery + Fire Arrows and Tactics/Cold Steel/Battle Balance.
3. If I'm leveling up an Elven Chaos Knight, I sometimes take Cold Steel, Archery, and Battle Balance.
P.S.: Yes... this topic really needs to be brought up again.