Kratos, Geralt, Ciri, and Atreus must fight each other's respective bosses
Kratos and Atreus: Ice Giant, The Crones, Nithral, Imlerith, Caranthir, Eredin Breacc Glas, The Frog Prince, Ofieri Mage, Olgeird Von Everec (pre Hearts of Stone), The Caretaker, Nightmare Olgeirds, Gaunter O'Dimm (Riddle Solving), Golyat, The Wicked Witch, The Cloud Giant, and Dettlaff Van Der Eretein (if succeeded Regis will be there to finish off Dettlaff)
Geralt and Ciri: Svartáljǫfurr, Mattugr Helson, Grendel of the Ashes and Grendel of the Frost, The Valkyries (Kara, Geirdriful, Gunnr, Olrun, Hildr, Rota, Gondul, Eir), Queen Valkyrie Sigrun, Hraezlyr the Dragon, Magni and Modi, and Baldur (post mistletoe).
Kratos is fully upgraded and in his maxed out Valkyrie armor set with epic enchantments and has the fully upgraded versions of his Leviathan Axe and Blades of Chaos along with all of his runic attacks/magic. However he's only allowed to use the Epic Talismans (Ex:Shattered Gauntlet of Ages,Talisman of the Realms, Aegirs Protection, etc.) instead of the other Talismans. Kratos can also use Spartan Rage. Atreus has his equipment and runic attacks fully upgraded and is in his Legendary Sharpshooter Garb
Geralt is in his Grandmaster Wolf armor and is fully upgraded. He also has his enhanced Witcher Mutations from the Turn and Face the Strange questline and has Aerondight. He can also use his Superior versions of his potion, oils, and bombs. Ciri is also endgame and in her alternate outfit.
After each boss is defeated the characters gets two hour interval until the next boss.
Who succeeds and why?
BONUS ROUND: Both parties must team up to get through the Shadow of Mordor/War universe and must fight Sauron, The Nazgul, Balrog, and a crap ton of Uruk. How do they fair