Secret Mission 4

Where to Find It: You'll find the entrance to this mission during Main Mission 05. Look for the Blue Orb Fragment stashed away in an alcove. From there, turn around and face the wall directly in front of you. Summon Nightmare, and he'll smash through the wall, revealing a hidden area.

The Fight Begins: Clear out the initial Empusas that appear in this new area. Once they're dealt with, you'll see some stairs. Climb them, and at the top, you'll find the red light. Step on it to start Secret Mission 4.

Enemy Waves: The mission throws Hell Cainas and Hell Antenoras at you in a pretty cramped arena. It starts with just one Hell Caina, but quickly escalates. Two Hell Antenoras will join the fray shortly after, and then more enemies will keep spawning. The key here is to avoid V getting hit at all costs.

V's Familiars: Relying solely on Shadow and Griffon won't be enough. You absolutely need to bring Nightmare into the fight. Keep an eye on your familiars' health bars; if they get into trouble, recall them by dodging to prevent them from being stalemated.

Prioritize Targets: Your best bet is to try and take down that first Hell Caina as quickly as possible, ideally before the Antenoras even show up. If you manage that, great! If not, don't panic. As soon as the Antenoras appear, summon Nightmare and have him help thin out the enemy numbers.

The Promotion Skill: If you've invested in V's skills, the Promotion ability is a lifesaver here. It lets you ride on Nightmare when he's summoned, and you're invincible while doing so. Summon Nightmare early in the mission, hop on his back, and you can attack with Circle/B while still controlling Griffon and Shadow with their respective buttons. This gives you a safe zone to operate from.