Entropy 3

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.