If you have followed the content link, but actually want information on how the equipment items of M&M:HO work, use following link: Equipment
NOTE: When adding/editing items and sets, please follow the Equipment Standardisation Guide.
Expedition Unique Items Edit
Heroic Unique Items Edit
Heroic Battle items stats and unit improvement is random(ish) and only bound by their artefact value, which in turn depends on which heroic tier you are battling on.