"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
Don't call me Grom!
Leader Ability
For The Horde!
All nearby friendly units gain .
Traits
Tank
Bloodlust
Melee
One-Target
Possible Army Slots
Talents
Bladestorm
Gain an AOE bladespin ability that damages all nearby enemies.
Mirror Image
Summon two fragile mirror images when entering combat.
Savage Strikes
Deal double damage to enemies who are below 50% health.
Recommended Build