The debate about ARMS amongst Nintendo fans is lit due to its launch beeing only 2 months away. Many think the game will pull off another Splatoon while others think it'll perform poorly due to beeing a Fighting game. In my opinion the success of Splatoon was caused by two major factors:

-The Global Testfire that created an enormous ammount of hype for the title by letting players try out the game;

-Nintendo's choice of heavily advertising the game, putting behind it an advertisement budget equal to that of Mario Kart 8 ;

I think that if this two points were to be applied to ARMS the game would definitely become a multi milion seller but in reality we don't know what Nintendo plans to do: there's certainly still time to make a Demo given that the Global Testfire took place only a few weeks before the launch of the game while on the Advertisement part it really depends on wether Nintendo thinks the game is worth it AND if they're capable of doing it, in fact ARMS is releasing only one month  and a half after Mario Kart 8 Deluxe and one month before Splatoon 2, the new iterations of the two most heavily advertised games on Wii U.

How do you think Nintendo will handle the ARMS advertisement ? Will we see a Demo announced before release ?

It will be advertised similarly to BotW (on a smaller scale). We will see Youtube videos, video ads, website ads, tv commercials, etc.

Even now, I still see Switch ads on strange places like Russia Today (it even pops up on my friends' devices). If Nintendo keeps up their improvements, things are looking bright

They are advertising it a lot on their Youtube channel, probably more than average, but less than Splatoon is my guess

I don't think its going to have nearly as much advertising as Splatoon. They made a statue for Splatoon. They had people out for a Splatoon event. They are not going to ask be to come out to box XD.

However, I think they are going to do a very respectable amount of advertising. Like Platina said, they already are on Youtube.

id say same as splatoon.

The same as MK8DX and I think it will sell more than Splatoon 1 but less than Splatoon 2


Also the game is on Switch, is a free promotion only for this, so...

They learned from Splatoon.

Given the stellar marketing the Switch had(and the overall quality since the Switch came into public), and the overall importance that Nintendo is giving ARMS, I would say that it will have the same push as the first Splatoon had.Actually, I even think it will receive a similar form of DLC treatment.

They better do some heavy marketing unless they want it to bomb.

You're a spring now! You're a Arm now! You're a Ribbon now! You're a Arm now! A-A-A-A-A-A-ARMS!