I would like to give my players the option of learning a way to make a spell or magical effect permanent. To this end I've created a homebrew spell, Spell Permanency (quoted below).
Before implementing this spell in game I would like to be aware of the potential ways in which this spell could be unbalancing and or exploitable. I have attempted to address some of the concerns raised by previous editions with limitations in the spell. These limitations may (or may not) be too severe.
5th level transmutation
Casting Time: 24 hours/level of spell being made permanent
Components: V, S, M (diamond worth 1000gp per level of the spell being made permanent, one willingly given attunement slot of the caster or recipient of the permanency spell)
While Spell Permanency is being cast the duration of the spell or magical effect being targeted is extended for the entire casting period. Once the casting has been completed the duration of the targeted spell or magical effect becomes permanent.
This spell can only make the duration of 3 spells, or magical effects, affecting the same creature permanent at any given time. For the avoidance of doubt, no creature can have more than three permanent spells or magical effects active on it at any given time. Any casting of this spell which attempts to make a spell, or magical effect, on a creature permanent beyond this limit fails.
During casting the caster must be in constant contact with the object or creature upon which the target is affecting. In the case of a portal being made permanent the caster must have one hand placed through the portal for the duration.
While casting this spell the caster is unable to gain the benefit of resting, and suffers all of the effects of lack of rest. While the spell is still being cast, levels of exhaustion gained from a lack of rest can be removed from the caster by Greater Restoration. After the casting has finished, these levels of exhaustion can be removed in the normal way.
Spells or magical effects that have been made permanent can have their permanency removed only by the use of the following spells: Wish, Dispel Magic cast at 9th level (dispel magic automatically fails if cast at a lower level), Greater Restoration (which only works if the creature who sacrificed the attunement slot is willing).
A spell or magical effect that has an alternate end condition will still end if that alternate end condition is met. For example a permanent duration polymorph will still end if the creature affected by it is reduced to 0 HP. Similarly a creature under the effect of a permanent invisibility spell will still end if the creature attacks or casts a spell.
If a spell or magical effect that was made permanent has it's permanency removed or ends prematurely the attunement slot used as one of the material components in the casting is regained.
Whether or not the casting of the spell is successful, the creature who gave up the attunement slot suffers three physical stresses which cannot be reduced or avoided in any way. These stresses remain in effect for 10d6 days. For each day the creature spends doing nothing but resting, eating and reading the total recovery time is reduced by 3 days.
- The creature immediately suffers one level of exhaustion, which is only removed at the end of the period of stress.
- The creature's Constitution drops to 3, if it isn't 3 or lower already.
- The creature's speed, for each form of movement, is reduced by 10ft. If this reduction would bring the creature's speed below 0 in any one form of movement, it instead drops to zero.
How balanced/exploitable is this homebrew spell?
Experience from other versions of the game where permanency was gamebreaking is welcome. Both in terms of how this homebrew potentially avoids those pitfalls, but also potential pitfalls it doesn't avoid.