Mini World Changes were implemented in the Winter Update 2011. Just as World Changes do, they allow for a more dynamic shaping of the Tibian world but unlike them, these cannot be triggered through actions made by Players. These changes happen somewhat rarely and do not come with warnings. They last a few hours. NPC Towncryer tells you about these mini changes, by shouting a message. Since Updates/10.2 it's also possible to check which MWCs are active on the World Board at the Adventurer's Guild.