Time your buffs and debuffs according to his A2 and A3
Avoid Turn Meter Increase and Turn Meter Decrease abilities (see his P3)
Beat him quickly (before he reaches 20 turns) or maximize survivability (if you exceed 20 turns)
The most important piece of the above is timing those buffs and debuffs. Grythion starts with his A3, which means that in Round 1 you should avoid placing buffs on yourself, else he’ll take them away. Right afterwards, he’ll use his A2, which means he’ll transfer any debuffs you’ve placed on him and fill up his Turn Meter. Generally speaking, place your buffs right after his A3 and place your debuffs right after his A2. After that, it’s a race to kill Grythion before he reaches 20 turns at which point his speed and damage goes off the charts. [HP Burn] works well to help bring him down steadily, as well as Warmaster/Giant Slayer. Cleansing debuffs with someone like Doompriest is also very helpful.
Team composition
The team I use is the following:
Iron Brago (lead): Iron Brago deals good damage, has a great aura and a great passive to increase DEF, and also casts Increase DEF on the team. One of the best Champions for Doom Tower survivability.
Scyl of the Drakes: Great champion aside from her Decrease Turn Meter on A1, which backfires due to Grythion’s P3. Good for survivability.
Doompriest: Great for debuff cleansing and survivability.
Rotos the Lost Groom: Bring him in for DPS, just make sure to avoid using his A3. Max out his HP using the A2, then just spam the A1 and hope for extra turns.
Lydia the Deathsiren: Clearly not the most achievable Champ, but great in almost any content and it’s no different here. Brought here for debuffs (just remember to time them correctly) and general DPS.
Here’s an alternate more achievable team (no Legendaries, and no Void Epic/Legendary champs):
Kael (lead): Kael’s a pretty good option for DPS here, and has an aura that’ll increase your HP to boot.
If you’re surviving till Turn 20 but not beyond that, swap out a survivability Champion for a DPS one.
GRYTHION THE CELESTIAL GRIFFIN SKILLS
A1: Shockwave. Attacks 1 enemy. Has a 100% chance of placing a [Fear] debuff for 1 turn.
A2: Rock Smash. Transfers all debuffs from Grythion to each enemy, then attacks all enemies. Fills Grythion’s Turn Meter by 5% for each debuff transferred. (cooldown: 3)
A3: Death Gust. Removes all buffs from all enemies, then attacks all enemies. The buff removal cannot be resisted. Damage increases by 10% for each buff removed. (cooldown: 3)
Passive 1: Divine Strike. Attacks an enemy whenever their HP drops below 50%. This attack places a 100% [Heal Reduction] debuff for 2 turns.
Passive 2: Celestial Bond. Adds one [Sky Bond] buff to Grythion at the start of each turn. Also adds on [Sky Bond] buff to Grythion whenever an enemy’s HP drops below 50%. Each [Sky Bond] buff increases Grythion’s: ATK by 5%; C. RATE by 3%; C. DMG by 5%; SPD by 2.5. Will ignore [Shield], [Block Damage], and [Unkillable] buffs when Grythion has 10 or more [Sky Bond] buffs. Can stack up to 20 [Sky Bond] buffs. [Sky Bond] buffs cannot be blocked or removed.
Passive 3: Fair Wind. Whenever Grythion’s Turn Meter is decreased, the Turn Meters of all enemies will be decreased by the same amount. Places a [Stun] debuff for 1 turn on enemies with fully depleted Turn Meters. Whenever an enemy’s Turn Meter is filled, Grythion’s Turn Meter will be filled the same amount. Turn Meter increases are tracked and counted individually for each enemy.
Passive 4: Almighty Strength. Damage from skills that scale based on Enemy MAX HP cannot exceed 10% of Grythion’s MAX HP.
Passive 5: Almighty Persistence. All Turn Meter reduction effects are reduced by 50%.