"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
Famed demigod and demihorse!
Leader Ability
Grovekeeper
Keep your friends healed and your enemies heeled.
Traits
Elemental
Tranquility
Brambles
Resistant
Healer
Ranged
One-Target
Possible Army Slots
Talents
Revitalize
Allies entering Tranquility trigger an additional heal pulse.
Force of Nature
Summon a Treant when a Rooted enemy dies.
Wild Growth
On deploy, Root all enemies for 5 seconds.