Spells rebalanced - a lot of spells were changed/polished; their mana costs, and damage outcomes are now more suited for both single and multiplayer difficulties. Missiles were changed quite extensively, and now are more damaging even when unboosted. They also seem to move faster, making them a bit more deadly (although it might be only an illusion). Because boosters are now reduced in power and capped, spellfights need thinking instead of spamming. Summons - aside from the previously mentioned changes - also last much longer (even when unboosted). The spell-level booster doesn't work on them anymore, so there is a reason (finally!) for using summoning boosters. Duration boosters now yield radically slower duration increase in time-unquantified spells (such as necropower, or lightning storm). Spell appearance in loot and at vendors is level-locked (so there are very, very slim chances of getting high-level spells too early), in addition necromantic spells appearance has been severely reduced in loot, and the appearance in loot now seems to rule over which ones are available at vendors (it seems that until you find some spells on your own, you are limited to very few basic spells from this school at necromantic vendors - this is also level-restricted). As before, you cannot become a grand master in the school before level 20, and cannot become Councilor before level 30. Magic is now properly challenging, and requires thinking and strategies (if you keep in mind new hotbar, new boosters, new staves and new summons).
Cloning removed - possibility of cloning/duping items in multiplayer has been fixed.
Summoning exploits for levelling and looting were also removed from both multi- and singleplayer (which is also mentioned in summons update above).
Self-made potions no longer stack in chest/shared inventory/trade interface in multiplayer, previously they occupied (those highest potions, using the "Fox Heart Potion" bottle) the same slot regardless of their properties and quantity. This makes trading/storage much more organized in multiplayer.