Note: This topic might be about less than 2 months late, but screw it!
For those who actually have the game, Blaster Master Zero, on the Nintendo switch, on November 25, 2017, version 1.5 was released with a new multiplayer mode called: "Blaster Battle Mode". This multiplayer mode is a 1v1 fight between 2 players.
And, if you buy some DLC characters, you can use them in this mode!
So, whatcha think. do y'all think there'll be a online mode in the next update?