Godsvivors

Apollo is unlocked by leveling up the Ignis skill to level 3 during a run. This skill has a chance to set enemies on fire when you shoot them. It's completely random if you get this skill presented to you as an option or not, and there is no rerolling in this game, so if/when you see it during a run, focus on grabbing it. Once you have it, you're more likely to see it available to upgrade. Get it to level 3 and this achievement will unlock immediately during the run.