Dimensions End: Entropy - Tier 3. This tier has No Enemy Resistances. Enemies have a lot of buffs, deadly AoE HP Attack on the 3rd wave and last wave. The recommended roles are Debuffers and Tanks. The bosses' total HP is 4,620,000. The turn requirement is 115. The DPT you need is 37K.
Wave 1 (Trash Wave)
Two Lunatic Spirits and One Lunatic Dark Skeleton. Note that the Spirits absorb Ice, Wind, Holy and Dark so be careful if you'll be bringing elemental characters. They can inflict poison, confuse and can restore their HP so you want to kill them asap.
Wave 2 (Trash Wave)
Two Lunatic Ghosts and One Lunatic Dark Skeleton. Prioritize the Ghosts then the skeleton.
Wave 3 (Boss Wave)
One Lunatic Marilith and One Lunatic Lich. The Marilith can inflict Poison, Fire Resist Down, mBRV down and most interestingly, Max HP Down. If you have Yuffie, you can use this to your advantage. Get that debuff on her (if I recall correctly the Marilith targets the unit with the highest current BRV after her turn), burst down the bosses and make sure that Yuffie has her EX charged for when the Maralith targets herself, as you cannot let her buff herself! RNG can be tricky, but if she reapplies the debuff to Yuffie again later in the wave, you can throw it on wave 5 - but this is *not* required. Just halving the HP of this wave is enough to run it with a fairly budget team, generally 3 ingots. If you are not using Yuffie though, you want to keep yourself unbroken. Having debuffers to wipe the Maralith's many generic buffs would greatly help. It has several ST and AoE HP Attacks. Never get broken by the AoE HP attack. The Lich is also dangerous with its ST HP Attacks and poison. You want to keep them broken at all times.
Wave 4 (Trash Wave)
Two Lunatic Dark Skeleton. No threat here just kill them off conserving skills.
Wave 5 (Final Boss Wave)
One Lunatic Tiamat and One Lunatic Kraken. Tiamat is weak to Earth while Kraken with Thunder. You want to watch out for Tiamat's Jet Burst which is an AoE BRV+HP Attack that inflicts SPD Down. Kraken also has ST BRV+HP Attacks and can get fast. Debuffers help remove their buffs. Keep them broken, consistently deal damage heal when necessary. You want to burst down Tiamat first as Kraken when broken is much more manageable.
Most Used Units. Ultimecia is the most used unit for this tier. With her free turns and high magic AoE DPT, she destroys this stage. WoL follows her as his shields saves you in multiple BRV breaking attacks of the enemies that can lead to your team being wiped. Agrias is wonderful here as well with her overall utility. Sherlotta with her healing. Lilisette and Faris with their debuffs and battery. Basche is an alternative tank. Serah with her offensive capabilities. Cait Sith and Rem with their HP healing and battery. Yuffie is a special mention as her mechanic allows you to cheese this stage.
EX Only Units. No surprise having Sherlotta and Serah here as they will be useuable with their base EX weapons in most if not all tiers. Leon with his gimmick can help cheese this fight.
Summons Used. Shiva is the most used as the Marilit boss is weak to Ice. Followed by Brothers as the Timamat is weak to Earth and Ramuh as the Kraken is weak to Thunder.
Top Unit. Ultimecia is the top unit for this tier. Having monstrous magic AoE DPT along with her free turns, debuffs and gravity shaving, she will definitely carry your team on completion of this tier. Paired with her, a tank like Warrior of Light would be great and debufferst such as Faris, Lilisette, Serah and support/utility units like Agrias and Rem.