The Queen's Rebuke

In her final moments of life, the Autumn Queen unleashed her rage, bitterness, and hatred upon Tairos in an act known as the Queen's Rebuke. She detonated her storehouses of Manacite and directed the destructive energies back into the Leylines. This single act incinerated her forest and her castle but the effects on the metaphysical world were far more dire. It was like igniting lantern oil inside the veins of a living creature.
The very conduits that carried raw magical energy to Tairos were scarred deeply and left to be infected by the types of death energy that fuels necromancy.
This had several very devastating and long-term effects on Tairos

1). Any creatures made purely from magic found their life essence cut off, effectively starving them. Outsiders of all kind became nearly impossible to summon and sustain. Demons, Angels, Elementals and similar entities needed to leave Tairos or find other sources of energy to maintain their presence. Elementals would flock to regions where their key element was plentiful. Demons and Angels would otherwise be confined to lurking within sites holy to them or possessing mortal bodies. Only outsiders fueled by death energy remained unaffected. They were already perfectly suited to sustain themselves off negative energy

2). The Silence of the Gods. The divine pantheon of Tairos used the leylines to interact with their mortal followers. By this pathway were they able to answer prayers and send fuel for the castings of their clerics and holy warriors. After the leylines were burnt the voices of the gods were silenced and their ability to interact with Tairos ended.

3). Magic became a fatal endeavor to attempt on any level. Without Manacite to draw upon pure magical energy the caster is left drawing upon unfiltered, raw, negative energy. Death energy. Opening one self willingly to this kind of power can quickly destroy a living body or corrupt a magical item's creation. Sometimes both. The only magic that remains unaffected is Necromancy. This type of energy is perfectly suited to fuel its brand of spells. (In game mechanic terms any caster attempting to cast a spell without Manacite must make a Constitution save with a DC of 10+1 per level of the spell. If they succeed they take 2D4 Damage +1 additional D4 per level of the spell. If they fail, they take 2D10 damage plus an additional D12 per level of the spell. This damage cannot be reduced by any means. Any caster reduced to 0HP from this damage is destroyed entirely)

4). Magic cast without manacite has become unpredictable and can often behave strangely. Some known incidents include fireballs that never stop exploding, haste spells that have aged their targets several years, slow spells that resulted in regions of frozen time, healing spells that also resulted in disfiguring mutations, scrying spells that have directly transported the caster to the area he's looking upon and teleport spells that have scattered the body parts of the caster across several miles. (In game mechanic terms any critical failures associated with spells will result in some kind of DM designed mishap. Any failed concentration checks a caster is called upon to make will result in a DM designed mishap. Any spell cast by a caster who dies from the damage described in point 3 above will also result in a DM designed mishap)

Every piece of manacite contains raw mana which can be tapped into and used to power spells. An Arcana check of 12 will allow a character to identify the number of "charges" the stone contains. Spells will use a number of charges depending on how powerful the spell is. Cantrips do not use any charges but the caster must still have manacite on his person. Spells with a level of 1-4 use a single charge, 5-8 use two charges and 9th and beyond will require three charges.

Manifestation

Casters who use magic without manacite to fuel their spells will display lesions, burns and weakness in some minor cases. In more severe cases they are consumed by sickly greenish flames from within. Casters that die from attempts to cast without manacite often violently erupt from within and release dangerous negative energy. In rare cases, these deceased casters will return as twisted spirits or undead

Localization

All regions of Tairos are affected by this. The Queen's Scar seems to be the region where the effects are most severe.