"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
Bane of the Scarlet Crusade
Leader Ability
Army of the Dead
Rivendare periodically summons Skeletons at buildings you control.
Traits
Tank
Armored
Elemental
Fast
Melee
One-Target
Possible Army Slots
Talents
Death Pact
Periodically sacrifice a nearby Skeleton to be Healed.
Skeletal Frenzy
Nearby allied Skeletons gain Bloodlust.
Chill Of The Grave
Summon Skeletal Mages instead of Warriors.
Recommended Build