You can continue casting spells even after you have run out of spell slots, but at a cost.
Each time you cast a spell after running out of spell slots you will gain an exhaustion level equal to the spell level plus one.
Casting a concentration spell will give you a exhaustion level equal to the spell level plus one and then one additional level of exhaustion per turn until concentration is ended.
You cannot cast a spell if you would exceed level 6 exhaustion and can only cast spells that you have prepared.
For example: If you have run out of level one spell slots and cast a spell at level one, once the spell has been cast you will gain two levels of exhaustion
you gain the exhaustion as soon as the spell has been cast and not when the spell ends. The exhaustion would not affect roles for the cast spell but for all subsequent actions.
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