There are a ton of other topics about Gilgamesh focusing on team building for elemental hits.

Yes, sealing gilgamesh's elemental attacks is important but the core of the battle is learning to stabilize as more shit hits the fan as the battle goes on.

Lets first look at the AI: https://www.reddit.com/r/FFBraveExvius/wiki/missions/trial/2-6

above 80%

The only element that can be sealed is holy, but this is a weak holy which is only 190% ST. His alternative moves are his basic move sets: 160% hybrid aoe, and 160% ST. Worse case scenario on this turn is 3* 160 aoe hybrid which could wreck your team off the bat. So, what is the optimal way to deal with the first phase?

Just have Cecil taunt and attack normally with the others so you can conserve mana..etc. By keeping holy in the attack table, you reduce the chance of the aoe hybrid attack and cecil having high light/physical defence will gladly eat the ST/Holy attack.

80% -> 50%.

This gets a little more interesting. When you hit a threshold his next move will always be a 500% hybrid aoe dispel ST Death.

You can pretty much guarantee that your units will be wrecked if you go into threshold without defending your defensive buffs are off. Not to mention you will most likely have a dead unit from the ST death. A common way people go into a threshold is to cast Golem for the extra damage mitigation buff.

Here is where the stablization needs to happen. Ideally in a single turn you want to do the following: Raise/Heal/Rebuff/Seal Fire/Water/Wind/Holy/Earth. Can this be done? Maybe if you're lucky enough to not have too many deaths, but if you can't do this all at once follow this priority:

Dual cast Refia can raise heal, if you don't have dual cast, you'll have to use phoenix down heal. Holy is still the weak 190% ST.. so we can ignore it for this transition. Fire/Wind is dangerous and annoying so they are higher priority in sealing. Water/Earth doesn't have too big of direct effect at the moment, so it can be de-prioritised.

It will always depend on RNG whether or not he decides to wreck you at this vulnerable state but leaving manageable things on the attack table is can lower the chance of getting killed by the non-manageable things (multiple AOE attacks). Once, you've stabilized You can go back to sealing all his elemental attacks for a more predictable damage table from him.

50 -> 30%

Transition is similar to the previous threshold transition. By now, you may be experiencing mana fatigue. Highly recommend you address any mana concerns before entering the threshold.

Stabilization is similar to the previous one except holy is now a 220% damage and can confuse. Your sealing priority should be Holy-> Wind -> Fire -> water -> earth.

30% -> 0

The last threshold is no different than the 50% one. Mana fatigue would be the biggest issue. Your sealing priority should be the same as before. Stabilize after this threshold and the battle will be yours.

Preparation: As mentioned before, the core of the fight is stabilization. If you rely on a single character to do all the sealing, you would run into trouble if that character happen to die due to bad RNG.

The following is my recommended party list for F2P players:

• Exdeath with Aero/stone/water materia -> Carbuncle
• Refia with fire materia -> Ramuh (highly recommend with dual cast)
• Luka for backup healing/water resist/water damage/defense buff
• Cecil -> Golem
• Bartz -> holy element blade/ flame tongue (if you have dw)
• Generic High dps attacker w/wo element weapon.

Throughout the fight exdeath can just spam the lowest level water and stone spells with his innate dual cast. He can cover wind/fire/light if the other unit can't.

Refia is the main healer, she will be healing most of the time and be the clutch light element from ramuh's banish.

Luka can provide the water damage/immunity/heals/mana regen if needed.

Bartz with his wind blitz can cover holy/fire/wind.

Generic Dps will be the one providing damage. Can be your whaler friend. Doesn't need any elements but if he does have an elemental weapon you can modify your setup a bit to take advantage.

Cecil back up healer, provide taunt and buff with his LB or esper.