Designed to be a solo-focused mage, Golbez is a tanky dark magic damage dealer with a VERY high short-term bulkyness + a damage absorption buff to essentially be a boss unit that's hard to take down.
Offensive-wise, he has wide area attacks and uses a mix of spells and instant attacks to inflict certain status effects or debuffs so they can be punished with Abyssal Quasar, a very high damage dealing spell that almost rivals Flare.
He works best in small maps where he can enter a fight pretty quickly to make the best use out of Sorcerer in Black Armor, but he may lack good answers to tanky and evasive enemies in his kit.
Synergy well with BR-Helena, since they both have large AOE and SPR debuff. He also quite durable, so he is suitable in frontline. Plus with Prompto's dark imperil from long distance, that's gonna be really annoying to deal.