Like its predecessor, Players will assume the role of the titular Monsters and will brawl against enemies in large destructible environments. Many of the features that were part of the original game appears here as well. However, improvements have been made.
The camera has been updated to be more active, eliminating blind-spots and frustration.
The Lock-On feature was improved for the gameplay. If a monster is close to or attacking the player it will target them instead of monsters in the distance. It can also be set to automatically target whichever monster has the lowest amount of health.
Natural Hazards can affect the player's abilities and weapons used by them. Any object can be caught on fire which when use can deliver extra damage towards the opponents. However most flaming debris can hurt the player. Another example, Water has two depth types; shallow water and deeper water which can impede monsters' walking speed.
Picked up objects can provide specific affects such as Cement Trucks can slow monsters. Animals are now included as these objects can act as weapons.
Powerups include cloaking and armor. Weather powerups are most unique. When activated, the weather in the level changes. Weather powerups includes Downpour, Thunderstorm, Snowstorm, Heatwave, Meteor Shower. 
THE STORY SO FAR...
Calm before the Storm
In a strange twist of fate, the very monsters who had threatened to lay waste to our planet had actually saved it from annihilation. Destroying both each other and the alien menace in their ferocious War of the Monsters, they had left the world damaged, but alive. For a time there was peace: the peoples of Earth breathed a collective sigh of relief and began to rebuild.
Then it began. All across the globe, the mutations continued. Unbeknownst to the human race, the crashing saucer that had brought Cerebulon to his doom had also blanketed the atmosphere with leaking alien fuel. With the extraterrestrial mutagen now airborne, chaos broke loose in every corner of the globe: the monsters, long thought to be dead, now revived with even greater strength than before. An entire new generation of monsters rose by their side, and worse yet, a familiar evil began to stir again. The second War of the Monsters was beginning, and this time, no one would be safe...
The story takes place in Adventure Mode which comprised of ten levels. Unlike War of the Monsters, the sequels takes a non linear story where players are presented with branching paths that allow them to experience different fights with every playthrough. Each time they advance they will be presented with three paths, which then branch out again to three more each. 
The player's monsters begins his/her story at Townseville where its invaded by Zorgulon. After defeating the first monster and two more depending on the paths taken, the monsters heads to Tsunopolis or Baytown East.
Trogul Boss: Defeating Ultra V, a UFO crashed upon the robot killing it. Emerging after were the Troguls, gremlin like mutants who the monster must confront. All of the Troguls were killed. 
Sentou I Boss: As the player's monster advanced towards Baytown East, Sentou I, a giant warship appears and attempts to defeat the monster only for it to be left in a fiery explosion. 
Confronting two more monsters, the monsters will either battle Oobloth or Decatun
Oobloth Boss: Oobloth confronts the monster. The Boss took on multiple forms including its first blob like form, the player's monster and finally an amalgamation of monsters. The creature was destroyed and reduced to a puddle. 
Decatun Boss: Decatun awakens after several Karkaros were killed by the monster. The giant crab fell and drowns into the ocean. 
After defeating the remaining monsters, the player's monster enters a hidden base ran by Cerebulon who after returning to his original size, begins amassing power to destroy the Earth. Cerebulon and the selected monster confronted one another in an intense showdown where a time limit occurs ultimately leading to either two possible endings.
1st Ending: If Cerebulon wins or hasn't been defeated before time runs out, the base will self destruct.
2nd Ending: The monster succesfully defeats Cerebulon. A miniature version of the latter tried to escape again but was crushed by the monster who roared in victory with the threat finally passed. When Adventure Mode is completed, an epilogue of the player's monster is shown.