Fortress de Gaulle Carnage Stage
Hopefully you have some high resistances, since there are four enemies with Kill With (Elemental) Evilities on this map, two of which are luckily right in front of you at the beginning (the two Behemoths). So, they should be your first targets and you should try to take them out on the first turn, due to the Diamond Knights near the top going into defensive mode as soon they as they can. Besides the two Behemoths, there are two Bastets and an Agni near your Base Panel, neither of which are particularly threatening, despite the former having Physical Boost.
Behind them, you will have a White Fox pegging you with Star spells, a Zombie with the annoying Regeneration Evility, a Thief that's immune to water skills, and two Imps that carry the final two Kill With Evilities (and gain a bonus to their stats from having no one adjacent to them). The next wave carries the troublesome Mothman, who should be taken out as quickly as possible to avoid being poisoned, as well as a Sage that has access to all four Tera spells, and a 100% boost in damage if she targets one character (Concentration).
The two Lady Samurai behind them aren't too bad, but one has Euthanasia, so keep your HP above 25% and the other has Head-to-Head, so turn your character around to make them face away from her. You already know what to expect from the Battle Masters and Space Knights, who have nothing special, as well as the Diamond Knights (who are probably already dead from defending). Save the boss for last, to avoid getting your DEF debuffed upon its defeat. The entourage behind the boss consists of four Maids (nothing special), a Saint (buffer) and a Sage, who is probably the biggest problem out of them, but not as bad as the other Sage on this map.
Flowerful Carnage Stage
One of the first things you want to do is get your Bonus Gauge to level 1 and summon your own Netherworld to get rid of the Netherworld Effect on this stage, which decreases everyone's wind resistance by 50%. As a threshold, enemy stats are starting to creep above 10 million starting with this stage, so if you've been having trouble, go back to the What's Next? section for details on how to make your characters stronger. Out of the first set of enemies you will encounter on this stage, the most dangerous is definitely the Unknown, due to its ailment-inflicting skills and Spreading Miasma making it easier for the ailments to stick. There will be two more Mothmen not far behind the first one, so keep a lookout for them.
The Rabbits on this stage can be quite dangerous, especially if your SPD is lower than theirs since they have a 30% chance to deathblow your characters if it is.. It doesn't help that they get a 100% boost to both ATK and SPD, thanks to Hidden Valley, so you can try to lure them to a lower area first to get those stats down further. As long as you try to keep the Parthenocissus' away from other enemies, you don't have to worry about their Evilities buffing them.
Succubi are always a problem because of Charm and one gets a 30% boost from the male units on this map, although you likely will thin out those numbers by the time you get to her. The other one can Charm characters adjacent to her at the end of the turn, so that one is definitely more dangerous, although they tend to stay away from you and hit you with spells. The three Nine-Tailed Foxes at the top, including the boss, don't have much, although the boss does have Magical Boost.
Gorgeous Carnage Stage
As you can see when you enter the map, your Base Panel is surrounded by a lot of enemies (the Dark Paladins and lower from the table above). The ones that stand out as being troublesome from the entire bunch are of course, the Diamond Knight (due to their defending), the Rabbit (in case your SPD is lower than theirs), the Bastet (because of Vendetta), the Space Knight, the Shadow Orc (because of Mass Psyche), the Azazel, and the Blade Master. Sitting behind them, on each of the stairs, will be a single Erato, with a big boost for their ice spells thanks to Icic-Hell Blessing.
The Chimeras are the only enemies on the map that provide a negative effect to your characters, which is the usual 5% stat decrease thanks to Evil Eye, plus they also have the ailment Deathblow chance Evility. The Parthenocissus enemies will Magichange with the Thieves on the first enemy turn, granting the Thieves the Sweet Aroma Evility, but the others are lost, so there's nothing to worry about there.
Three of the four Twin Dragons will have Hypered, meaning they will always be giants (their moveset is limited, though). One has Double Attack, meaning their damage will increase if they attack the same character on a subsequent turn. They only have one water-elemental skill, but another has Icic-Hell Blessing, as well as Auto Recovery. The boss has a boost to both physical and magical attacks, as well as Imperial Wrath (you hit them with a critical and their next attack is 100% more powerful) and Icic-Hell Blessing.
Outer Dark Demise Carnage Stage
The first two enemies you will fight with are the God Busters, who have one extra range on their normal attacks and combined with Physical Boost and No-miss Counter, they can be annoying for melee characters. Behind them is a Diamond Knight, who will have some extra firepower thanks to the Agni Magichanging with her on the first turn. You should be used to the Knights by now and know the dangers of leaving them alive longer than they should be, so hopefully you can take her out on your first turn. The Liliths will likely sit back and hit you with Tera-level spells, but be wary of their Charm abilities, too. The Twin Dragon near them is equipped with Hypered, making it always be giant, but it's not too bad since its moveset is limited to one skill.
One of the Shadow Masters has Bad Trip, making him more deadly than usual if he manages to inflict you with an ailment. The Mother Brains will likely do their usual buffing, which can be problematic since their buff spells are pretty good. The Odins are nothing but beefy tanks, although two of them have Physical Boost equipped. The Sages will have extra firepower help from the Eratos, who Magichange with them on the first turn (Lovely Song is more of an overall nuisance than anything helpful for the Sage herself). None of the other enemies are anything too special, although the Boss is a Chimera, meaning that you have to contend with your stats being lowered by 5%, plus it reduces your dodging by 20%, has 20% boost to all elements and access to all Tera-level spells.
Evil God of Tyranny
This is the final battle in the Carnage quest line and has you facing off against a very powerful foe. Carnage Void Dark (as he's commonly called) has around 50 million in all of his stats, and roughly 3 billion HP. He's surrounded by a bunch of enemies that have stats ranging from 25-35 million each, but the catch is that they don't even really matter, as the battle will end upon defeating Void. It's very possible to defeat him with stats around 40 million, so you don't need to do too much else than what's described in the What's Next? section. Note that you will want the four characters with Evil Eye and Angel Song for this battle, one of which is a Professor with a maxed out buff (Braveheart for physical and Magic Boost for magic).
To start off the battle, place a throwaway character on the middle panel on the first "step" leading down. This will lure Void into coming near your Base Panel on his second turn, without you having to worry about the other enemies interfering. Once Void is near your base, it's time to bring out your characters. Start by surrounding the base panel with the four characters with Angel Song/Evil Eye. If one of them isn't a Professor, bring her out and place her somewhere; do the same thing with a Maid (insurance in case you don't kill him) for an extra turn with Afternoon Tea.
With the base deployment of 10, you should have five characters out on the field, and one more dead, leaving at the most four left. Bring out Archers and have them all attack Void to build up the combo so your main attacker gets a boost to their own damage. If you don't kill him on the first turn, then use Afternoon Tea on your attacker and try again (without the Archers this time). You can also bump up the deployment count by passing the All-Out Attack bill in the Dark Assembly, allowing you to bring out 20 total characters.
Note: Defeating Carnage Void will unlock three different things, with the main one being the final Unique Evility slot for the character who delivered the final blow. The second thing will be the Dimensional Devastation trophy and the last is the More Carnage Gear option on the second page of the Cheat Shop. This makes enemies in the Carnage Item World have more equipment.