A couple of updates from the ARMS Twitter account: first of all, they revealed another alternate costume, namely the dark-colored Ribbon Girl you see above. They also posted a screenshot of the “Arms Lab” stage as well as the next weapon showcase video, featuring the shocking Sparky:

電気のアーム「スパーキー」！
チャージすると、内部の発電装置があらわになるアブネー逸品！
リボンガールも愛用中で、身も心もシビれるパンチを放ちます！
旧型「サンダーパンチ」を改良した、最新モデルです。 pic.twitter.com/9Cl9CcHKq7

— ARMS（アームズ） (@ARMS_Cobutter) April 25, 2017

Source: http://nintendoeverything.com/arms-ribbon-girl-alternate-costume-sparky-weapon-showcase-video-arms-lab-stage-screenshot/

Here's also the alternate Ninjara which has already been revealed;

The game keeps looking better and better. I recently watched a treehouse video with a friend and both think the game looks awesome. Can't wait for June! Hopefully it'll be good and not a dud in the end.

Man, i can't wait to play this game!

I don't think it will be included in this first title, but I'd really love slightly larger multiplayer (8-16) with strategic mapping that makes various different types of ARMs characters useful depending on the situation.

This actually looks like a super fun game and concept if they really go all in on it. I imagine we'll have to wait for ARMS 2 for that.

Looks good!

Once upon a time, I couldn't care less about this game. Now, with good reviews (75%+), I can see myself buying it. 85% or higher and it's a day one purchase!

That ribbon girl custome looks awesome.

Browsing this thread makes me hear the reveal trailer theme in my head.

Mega charizard x

Nice, wonder if there will be more than 2 colour sets