Secondary skills are beneficial qualities of heroes. There are 28 different secondary skills and each one has three levels: basic, advanced and expert. Each level increases the capability of the secondary skill making it more influential. Typically in custom scenarios heroes start with either two secondary skills at basic level or one at advanced level. Each hero can have up to eight secondary skills.
If a hero does not already posses eight secondary skills, he/she gets an offer of two different skill during level-up. The first offer is a skill s/he already posses but which is not yet at expert level. The second offer is random, but the probabilities of the skills offered are dependent on the hero's class. If a hero already has all secondary skills at expert level, both offers are random. If a hero already has eight secondary skills, both offers are random but within the skills hero has.
There are few other ways to acquire a secondary skill. They can be learned from scholars, witch huts or universities on the adventure map. In Armageddon's Blade Conflux has a special building magic university that can teach one of the four schools of magic. Additionally, at map editor it is possible to set events on the map, that teaches secondary skills.
Once secondary skill is learned, it can not be removed. Although in the original Restoration of Erathia there was an adventure map location called market of time, which supposedly was intended to allow hero to "forget" secondary skills. However, the fact that hero can not remove secondary skill, makes the choosing of them one of the most important decisions in the game.
Secondary skills are divided into three categories: combat skills, magic skills and adventure skills. Combat skills affect directly to combat capabilities of creatures under hero's command; magic skills affect hero's abilities to cast spells; and adventure skills improves hero's adventure map qualities.