The 5-6 player Ice Storm expansion pack adds 2 new characters, 3 new locations, new spells/counterspells/companions, and some new mechanics into the game (in particular, freeze and stun status effects, which is why it comes with status effect tokens). It does let you expand the game for up to 6 people, but the 2 new characters and hex tiles can still be used even instead of characters and hex tiles from the base game even if you're playing with fewer people.