"Army slots" are the bottom 3 slots in each build. They are awarded from successful dungeon completions and every leader has a distinct pool of options. Each slot can be changed after unlocking by spending Arclight Energy.
Summary
Riding dragons before it was coool
Leader Ability
Blacken the Skies
Your other troops cost1 less
Traits
Dismounts
Elemental
Flying
AoE
Possible Army Slots
Talents
Flaming Soul
Cast Living Bomb upon dismounting, damaging nearby enemies.
Scale and Steel
Gain Resistant while flying and Armored while dismounted.
Legionnaire
Dismount when first taking damage. The Drake continues fighting.
Recommended Build