This effect is my interpretation of the D&D spell Spirit guardians. The spellcaster casts an aoe spell that summons forth demons that protect the user by attacking anyone inside the radius. This Spell normally depends on the alignment of the character, so It can either be holy, with angels attacking, or in this case, an unholy warlock type of spell, with demonic beings attacking.
Thanks to Neal Wojahn, Kristy Doan, Eric Young, and everyone else who helped give me feedback on this piece!
I had a lot of fun making tons of shaders and animating those tentacles!