List of bonus sources
From VCMI Project Wiki
List of all possible bonus sources
*ARTIFACT *ARTIFACT_INSTANCE *OBJECT *CREATURE_ABILITY *TERRAIN_NATIVE *TERRAIN_OVERLAY *SPELL_EFFECT *TOWN_STRUCTURE *HERO_BASE_SKILL *SECONDARY_SKILL *HERO_SPECIAL *ARMY *CAMPAIGN_BONUS *SPECIAL_WEEK *STACK_EXPERIENCE *COMMANDER *OTHER