You must scale Baelsar's Wall to reach the Griffin and stop his plan.
How to Unlock
The Baelsar's Wall 4-player dungeon is unlocked by the level 60 Main Scenario Quest Griffin, Griffin on the Wall.
Clear All Barricades
Defeat enemies, and one of them will drop an Imperial Identification Key. A player needs to pick up this key. Once it has been picked up, any player can open the Security Terminal. Be sure to pick up each key that drops so you can open each Security Terminal in your path.
Magitek Claw is a high-damage attack on the player highest on the enmity list.
Sky Armor Reinforcements will sometimes appear, chaining a random player. The chained player will be hit repeatedly by Magitek Hook. Kill the Sky Armor Reinforcement to stop this attack.
The Magitek Predator will target a random player with Magitek Ray, a line attack.
A random player will be marked with a red indicator over their head, and will soon be hit by Magitek Missile. This attack will hit any players nearby, so the marked player should stay away from other players.
The Armored Weapon attacks with Launcher, which damages all players.
Dynamic Sensory Jammer gives you an Extreme Caution debuff and places three red markers around you. If you are moving, auto-attacking, or using an action when the Extreme Caution debuff wears off, you will be hit with Dynamic Sensory Jammer, a high-damage attack that launches you into the air. Be sure to stop your auto-attack by putting your weapon away (go to the official site's Basic Controls page and search for "Draw/Sheathe Weapon/Dismount" if you do not know how to do this), and don't move or use any actions until your debuff is gone.
Magitek Bit summons untargetable bits along two of the edges of the area. These bits will each perform a line attack across the area. Move into one of the safe areas to avoid the attack.
When Armored Weapon casts Distress Beacon, many Magitek Slashers will appear. Kill them quickly to reduce damage to the tank.
Diffractive Laser is a circle attack.
Beak of the Griffin damages all players.
Flash Powder is a gaze attack that inflicts an Accuracy Down debuff on characters who are facing the boss when this attack finishes casting. Turn your character to face away from the boss to avoid it.
The Griffin will jump back and cast Sanguine Blade, an attack that covers most of the area, except for the area behind him. Quickly go behind him to avoid the attack. Sometimes he will jump more than once before he starts casting Sanguine Blade.
Claw of the Griffin is a high-damage attack on the player highest on the enmity list.
The Griffin will begin casting Lionshead, which has a long cast time and inflicts damage on all players when it finishes. While The Griffin is casting Lionshead, all players will be hit with multiple hits of Gull Dive. Afterward, many Blades of the Griffin will appear around the area, and each one begins casting Corrosion, a circle attack centered on each sword. The party should all attack the same blade to try to destroy it before it finishes casting Corrosion, giving players a safe location to stand in. The boss will sometimes cast Flash Powder during this time, requiring players to turn their characters to face away from the gaze attack while also attacking one of the swords.
Sometimes, while you are attacking a blade to create a safe area, a random player will be targeted with Big Boot, indicated by a red marker over their head. This is a knockback attack on the targeted player. If you are targeted with this, be careful to position yourself so you will not be knocked into an attack marker, or just use a knockback prevention move such as Arm's Length or Surecast.
The healer will sometimes be trapped by Restraint Collar. The other players should destroy the collar as soon as possible.
Completing the Quest
Defeating the boss will complete one of the quest objectives for the Main Scenario Quest Griffin, Griffin on the Wall. There will be a cutscene. This one is important, so it is recommended to watch it either now or via the Unending Journey in an inn room.