Mage's Last Stand

Mage's Last Stand allows a caster of any level to exchange life force for an extra spell slot. This ability can only be used if the caster is completely out of usable spell slots for to cast the spell they'd like to cast (i.e. if they want to cast a 5th level spell, but have a 6th level spell slot available, they cannot use this feat.)

• Once per day, a free action, a caster can choose to exchange one or more of their hit dice for a spell slot of spell level equal to the number of hit die they spent (i.e. a 3rd level spell slot would cost them 3 hit dice).
• The spell slot must then be used during the same round the caster used Mage's Last Stand.
• At the end of their turn, the caster takes necrotic damage equal to the roll of the hit die they spent to cast this spell, and their hit point maximum is lowered by the amount of damage they take until they have completed a long rest, (i.e. if they take 15 damage, their hit point maximum is lowered by 15.) This damage bypasses all resistances and immunities.
• At the end of their turn, the caster is also hit with a wave of exhaustion, and they must take one point of exhaustion for every two levels of the spell slot they received, rounded up (e.g. 4 levels of exhaustion for a 7th or 8th level spell slot. 5 levels of exhaustion for a 9th level spell slot.)

This feat was adapted from Burning Desperation by user Galaxiebot.