Underground Colosseum is a quest in Chapter 9, "The Town That Never Sleeps", in Final Fantasy VII Remake. As Cloud Strife and Aerith Gainsborough search for a way to enter Don Corneo's mansion and find Tifa Lockhart, they find they are unable to enter unless Aerith suits Corneo's taste. Having talked to Madam M, she enters Cloud in a tournament to earn enough money for a dress for Aerith.
The Corneo Colosseum is located on the south end of Wall Market, just before the Don's mansion. Talk to the staff inside, and he will enter Cloud and Aerith as a team. Enter the elevator to the colosseum downstairs. After a cutscene, the first room on the left contains a vending machine and a bench, while Johnny is found injured in the second room. After talking to him, Cloud and Aerith are announced.
To prepare for the first of four battles, equip Fire Materia and Ice Materia on either character, as the two enemies fought are weak to one or the other. On either Aerith this can be paired with a Magnify Materia. Cloud can benefit from linking the materia with Elemental Materia. Ensure Healing Materia is equipped on both characters.
Talk to the gatekeeper to enter for the battle is against the Beastmaster and two bloodhounds. All three enemies are deadly in close combat, meaning Aerith should stay back and kite around them, while Cloud guards against their attacks before unleashing his own. The enemies are easy to stagger and then lay into them with attacks. After defeating them, return to the waiting room for the next match. Use the bench to heal HP/MP, and then return to the gate.
For the semifinal match, Beck, Burke, and Butch are fought again, along with eight Corneo lackeys. A similar materia equipment as before applies, as fire materia is very effective against all enemies. Casting Fira against them, when clustered together, can defeat them quickly, while character abilities pick off the rest. After returning to the waiting room, a cutscene commences.
The final match is against a Cutter and a Sweeper, meaning that Lightning Materia paired with elemental on Cloud and magnify on Aerith is ideal. Casting Thundara can deal significant damage and pressure them, though the Cutter will respond by silencing with red smoke; dodge this attack immediately to continue attacking. Destroying the Cutter's right and left blade can pressure them easily, allowing them to be staggered shortly after and then destroyed.
Bonus match boss
After the final match, a cutscene commences, and Don Corneo demands another match. Use the bench to heal, restock on items such as phoenix down, and then speak to the gatekeeper. This battle is fought against the Hell House, which is weak to Ice in its default state, meaning equipping ice materia can be useful; however, this should not be relied on or paired with elemental materia, because it can switch affinity.
Instead of pairing any materia for elemental materia, one strategy is to equip more magic materia on both characters for more options, while another is to use the non-elemental Poison Materia to deal damage. Summoning Materia can also be used for this battle, meaning Shiva Materia should be equipped for her ice damage. Revival Materia should also be equipped on one character; Aerith is a good choice, as she is more often safe from damage and from its Hospitality attack by staying at a distance, though Cloud has more HP.
Hell House attacks with a salvo of ranged flaming attacks, and can leap towards a character to deal damage. It also resists damage from Cloud's swords, meaning that Aerith will deal most damage with her attacks, while Cloud simply attacks to fill his ATB gauge. Cloud can make use of Focused Thrust often to help stagger it, and magic spells can greatly increase the stagger gauge (if using ice spells, wait until after it uses House Call). Hell House is also capable of grabbing a character that is close with Hospitality and binding them; switch to the other character when this happens, and heal them after they are released. Hell House can shift its elemental affinities to be weak to a different element but absorb another; when this happens, use non-elemental abilities with Aerith until it switches back to being weak to ice, and if Shiva is ready, wait until it switches elements back to cast her.
After losing a third HP, Hell House becomes more aggressive, with more powerful melee attacks, and more often uses Hospitality. At one half of its HP, it becomes especially deadly as it can use God House Mode, creating a physical barrier. This means physical attacks from Cloud bounce off it while Aerith's attacks are reduced; however, when this ends it will become more vulnerable to being staggered. Avoid its attacks, and then use the opportunity after its God House Mode ends to cast magic spells. When it uses Jetstream, stand back as far as possible. If Cloud's Limit is up, save it for when the boss is staggered or God House Mode is not imminent.
Once it is down to one third of its HP, it can fly in the air more often. After flying in the air throwing bombs, it will then use Hellbound and crash to the ground. Other than avoiding attacks, the tactics are the same; use spells when its God House Mode ends to stagger it or deal significant damage.
Once Hell House is defeated, Cloud and Aerith are taken upstairs. After this, the player can compete in Corneo Colosseum battles at any time by going downstairs. To continue with the quest, return to Madam M's massage parlor in the northeast. She will offer to give Aerith a dress, but warn her that the two cannot leave the town after. This leads to "Parting Ways".
Hard mode tips
The first few matches are not significantly harder than those in a normal playthrough, but it is crucial to save or restore MP throughout them. Aerith can use Soul Drain offensively, and any spells she uses should be on materia paired with MP Absorption Materia. Avoid healing if possible, and instead of healing between matches, use the bench to restore HP. Cloud should use Provoke Materia to protect Aerith, and Aerith can equip First Strike Materia and/or Whistlewind Scarf to open matches with Arcane Ward and a powerful spell. This allows the match against the Cutter and Sweeper to be finished quickly by destroying the Sweeper with Thundaga as the spell begins.
The match against Hell House is the biggest combat challenge of the chapter, meaning conserving MP is unimportant, although using MP Absorption materia on Aerith is still ideal to last this battle. This battle is changed significantly, as the Hell House summons three tonberries throughout the battle, and if it wages too long, a Sweeper and Cutter can appear.
Refocus Materia allows a character to build up ATB very quickly. For summoning materia, Bahamut Materia is most powerful while also being non-elemental. Equipping Steadfast Block Materia is useful to resist more damage, and both ATB Assist Materia and ATB Stagger Materia can be helpful. Equipping Prayer Materia is effective for emergency healing, and along with this, ATB Boost Materia allows this to become available more quickly. Other options are to pairing healing materia with Magnify Materia, or simply using Spectral Cogwheel on Aerith with her limit break set as Healing Wind, allowing her to use it more frequently with how often she casts spells. Time Materia is extremely useful to allow Haste to be applied, and this also can be paired with magnify materia to cast the spell on both at once.
As before, with offensive magic materia, there are two approaches: either equip poison materia to cast spells that deal damage regardless of elemental differences or simply equip materia for all four differences to exploit all weaknesses. For instance, equipping each the four magic materia on Aerith, and one poison materia on Cloud, is effective. If elemental materia is used, it should be used on armor to defend a character, rather than offensively; pairing it with fire materia can resist Hell House's Jet Stream attack. As usual, HP Absorption Materia and MP Absorption materia are good pairs for offensive materia.
Casting Haste and Regen on both at the start of the match can be a great way to open the match. Against the tonberries, Cloud should use Triple Slash to destroy them quickly. Cloud can be used for curative spells, while Aerith casts spells offensively. As Hell House resists physical damage, most of Cloud's regular attacks will be against the tonberries. Use the medium-level spells in the first phases, and the low-level spells in later ones, as high-level spells take too long to cast.
When Hell House begins using God House Form, the fight becomes considerably more challenging due to the smaller window of opportunity to deal damage after God House Mode ends. During this phase, cripple its arms and cast spells against it during any windows of opportunity. In the final phase, cast spells to kill it as quickly as possible before it summons a Cutter or Sweeper.