Bone Cage

5th-level biomancy*

Casting Time: 1 action
Range: Self (20-foot-radius sphere)
Components: V, S, M (the bones of at least one non-animated corpse, which the spell consumes)
Duration: 1 minute
Class: Cleric, Druid, Paladin, Warlock, Wizard

You draw the bones from all corpses within range, forming a carapace of ribcages and femurs. You gain temporary hit points for each Small or larger corpse wholly or partly within range, according to its size, that last for the duration:

Size	Temporary Hit Points Gained
Small	1d6+1
Medium	1d8+2
Large	1d10+5
Huge	1d12+12
Gargantuan	1d20+25

As an action on a subsequent turn, you can cause your armour of bones to erupt, expending all remaining temporary hit points. Each other creature within range must make a Dexterity saving throw, taking piercing damage equal to your expended temporary hit points on a failure, or half as much damage on a success. Whatever the manner in which the temporary hit points are lost, the bones shatter and can’t be used in this way again.

At Higher Levels. When you cast this spell using a spell slot of 6th level or higher, the radius of this spellincreases by 10 feet for each slot level above 5th.

*can be replaced with necromancy
Source: Heliana's Guide to Monster Hunting