Undead Fortitude

You touch a willing creature who isn't wearing armor. A spectral skeleton seems to envelop and enter the target, and a protective magical force surrounds it until the spell ends. The target's base AC becomes 13 + its Dexterity modifier. The creature also gains the following effects of undead resilience:

The target gains 1d8+(your spellcasting modifier) in temporary hit points. While it retains these hit points, it has a +2 to constitution saving throws, and resistance to Necrotic and Poison damage.

The spell ends if the target dons armor or if you dismiss the spell as an action. When this spell ends, the target must make a Constitution saving throw or become violently sick for a turn, using its action to vomit.