Tortoise Shell

Tortoise Shell (Spell)

Difficulty: Easy

A simple spell with a simple name and a simple effect, Tortoise Shell causes the target, either the caster or a creature they touch, to have their torso bulk-up and harden into a tortoise-like shell, complete with a simple pattern. Non-magical torso-wear is destroyed, while magical equipment is absorbed for the spell's duration. Said duration is one hour, and should the target be within thirty feet of the caster when the spell expires, the caster can extend the spell another hour without need for repeat casting, though the still need to pay the energy cost.

The shell is extremely strong, and provides excellent protection to the torso, and the subject can fully retract any part of their body into the shell. On the other hand, the shell is also quite heavy, and is certain to slow and encumber the subject.Miscast:

01-20	The caster suffers a mutation that lasts until cured.
21-40	The caster or target (50% chance of either) is transformed into an ordinary turtle for the spell's duration, though they retain their mind.
41-60	The shell is not hard, but rather soft and fleshy. While still encumbering, it provides no protection.
61-80	The spell affects a random creature within 30 feet of the caster.
81-100	The caster and target both suffer a mutation for 24 hours.

Mutations:

01-30	The mutant develops a turtle-like beak and a short tail.
31-50	The mutant becomes cold-blooded.
51-60	The shell becomes permanent.
61-100	The mutant develops scaly patches over various parts of their body.

Bonuses:

The shell is surprisingly light and sleek, and doesn't slow the subject much.

The spell lasts 24 hours.

The spell affects 2-6 creatures within 30 feet.

The subject's skin becomes scaly and leathery, further increasing defenses.

For D&D 5E

Tortoise Shell
3rd level transmutation
Casting Time: 1 action
Range: Touch
Components: V S M (a scale or piece of shell)
Duration: Concentration, up to 1 hour
Classes: Druid
You touch a willing creature, and they grow a heavy, tortoise-like shell, merging with any armor they're wearing, and their skin becomes tough and scaly. Until the spell ends, the target's AC can't be less than 18, but their movement speed decreases by 10 and they suffer disadvantage on Acrobatics skill checks. As an action, the target may pull their limbs and head into their shell. While so withdrawn, they have resistance to all damage types except psychic, but can take no action other than extending their head and limbs, which takes another action.