A creature you touch gains an adaptive shield to protect them, this can look like a shimmering glow, hardened skin, or be completely invisible. While they have this shield, whenever they take damage, they gain resistance to that damage until the end of the next round. If they take that damage type again while they have resistance, they gain immunity. If they take a different type of damage before the resistance wears off, they lose the resistance to the first damage type. If concentration is maintained for the entire duration, the spell has a 50% chance to last another hour without costing an additional spell slot, up to 6 hours.
At higher levels: When this spell is cast with a spell slot of 4th level or higher, it can provide resistance to an extra damage type for each spell level above third. Additionally, if cast with a 5th level spell slot or higher, the resistance lasts for twice as long.
NOTE: this was something I made for a particular boss, and will probably give to other bosses that also have a little less hp. I have no idea if it would be balanced the way I have written for a player character.
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