Modes
Story Mode

The Story Mode featuring the Double Dragon, Billy and Jimmy.
It is a continuation of the story in Double Dragon II: The Revenge, and features all new enemies! Defeat the on-rushing attackers, and try to clear all the stages!

The game can also be played with a friend! (When first playing the game, Billy and Jimmy are the only selectable characters, but finishing all stages unlocks Tower Mode. Play this mode to unlock enemy characters for use in Story Mode.)
2P Duel Mode

This is a two-player battle mode!
Progress in Story Mode to unlock extra characters for use in this mode!

In this mode even enemy characters are selectable! They possess different skills to those seen in Story Mode, so try playing as all sorts of characters!
Tower Mode

Defeat enemies to advance as far as you can up the tower!
There are no continues! How far up the tower can you make it? New playable characters useable in all modes will unlock depending on the number of enemies you manage to defeat.

Progress in this mode and you may even unlock a certain fan favorite character!
Share Play (PS4-Only)
Double Dragon IV has Share Play functionality!
Share Play is a feature that lets you play Double Dragon IV with a friend even if they don’t own the game! Press the Share Button on the DualShock 4 wireless controller and send a game invitation to a friend to enjoy the game together or get help on a stage you can’t clear.
To use Share Play to play with another person, both parties must be PlayStation Plus members.
When using Share Play, there is a one hour time limit for each play session. When an hour has passed, the visiting player’s play session will automatically end.
Read more at
http://gematsu.com/2017/01/double-dragon-iv-details-background-modes-characters#wBphwjwvb0roOFr2.99