The Another World is a new world added in version 1.2. It is currently the hardest world in the game, it's unlocked once you complete the first stage on World 1. It has a green background.
Stages
Different from other 2 Worlds, this one has 6 Normal Stages and 7 Boss stages.
The Normal Stages are always unlocked and Boss stages are Unlocked one per day by 24 hours.
The Highest Difficulty level is HELL
Reccomendations for Last levels In boss Stages
As the Boss stages are Insanely difficult due to having multiple bosses and short levels, you must have some Home customizations like high level base HP, AP buildup, unit production and Metal Slug Production and Damage.
But what is important is the base HP. Almost every time, the bosses will get to your base, and with no Fallback it is hard to survive enough to have good units there
For the Dragon Nosuke Stage, have a Tall Tank unit like NOP 03 Sarubia, because gatling shots are extremely dangerous and sandbags cant cover from direct base hits. The Nop 03 Sarubia is capable of blocking these shots due to its tall hitbox.
For the Tetsuyuki and Jupiter Kings Stages use units that become invulnerable during their special attack, Like Shielded Soldier, Shielded Guerrilla, Mars People, Giant Snail and Leona, so you can get to the Boss and destroy it relatively Easy. If you don't have those units, try using fast moving units so you can damage the boss before it uses its laser attack.
For the Cloning Monoeye Stage Try Using Self Destruction units like Hopper Mecha or rebel Zombie, as they has high HP value and good resistance can make the Cloner fallback and giving more space
For The Dual Iron Nokana stage use Cheap and tank units, as they come whit a Abul Abbas he will eat the first damage you make in the short line, Iron Nokanas are Tank Units, so they cant make fallback and this makes very hard to win if they got to hit base
For The Huge Hermit use only range Units AND DO NOT USE SELF DESTRUCTIVE UNITS, as they cannot harm the giant crab. Huge Hermit destroys the road leading to the player's base, making self-destruction units useless (Right before he destroys a piece of road he kills every unit that is on that piece). The recommended untis are Trevor, Iron ISO, Hyakutaro and non-sandbag static units. Also try using long ranged units.
For the Shoe & Karn Stage use high HP units and self destructive units, also, try using units with long range, high HP, or special attack invulnerability.