The Occult Legionary is an alternate-stat version of the Ferverian Legionary. Instead of each figure providing Death Cloud, each pair of figures provides the Elusive ability. Occult comes from the Latin verb to hide. The armor tanks on the Occult Legionaries are filled with smoke instead of poison gas. The smoke obscures the air around the unit, making it harder to target.
Wells Expeditions have posted the details of an alternative stat version of the Roman Ferverian Legionary figure for Arcane Legions. From their website: