Dark Empowerment

Beyond material world, there are mysteries terrible to behold. Draw them in, and take them for your own.
You channel dark energy into your body, distorting your form and making you fearsome to behold. Your size increases to Large if it is smaller, and your equipment grows to suit your expanded form. If there is insufficient space, you grow as large as you safely can. While in this form, your weapon attacks inflict an additional 1d8 damage of their normal type and you gain temporary hit points equal to twice your spellcasting modifier at the start of each of your turns that last for the duration of the spell.