Awakening of Evil

And also, it seems this mod changes the game; in other campaigns, when moving to the next mission, the hero gains +4 or more to each stat. Does anyone else experience this?

This is not related to this wonderful campaign. It happens in older campaigns where assembled artifacts do NOT carry over to the next mission. For example, in the original campaigns for Railegh, Faydaen, etc. There are three sets that add stats to the hero: the Necromancer set, Rune Power (+1 to all), the Demon set, Urgash's Will (+5 to Attack), and the Dragon Power (+1 or +4 to all stats for 2 and 6 items).

If at the end of a mission, the hero has bonuses from one or more of these sets, then in the next mission, the artifacts disappear, but the set bonuses (but not the artifacts themselves) in the form of stat increases remain. These free bonuses can be obtained repeatedly when transitioning between missions. The Orc set does not have this glitch because the +3 to attack is given not to the hero, but to his troops (a hidden bonus, not visible in the tavern and not increasing the ballista's power).