Even the trailer itself shows hints : the way they show word by word " Jammies mode is here, " similar to " everyone is here " from the direct.
Announcing that " A new transformation has appeared " similar to the way Smash games would announce a new foe.
Lastely, it says that they specifically made this free DLC because they want to thank the fans... Thank the fans for what ?
Perhaps for making Shantae possible in smash through our determination and votes ?
And then we know about the conversation with Mimic, the words "Ultimate" and "Everyone" ( which are the trademark words of this iteration of smash )being used a lot as well as the word "invitation" because Shantae aims at handing invitations through the mode, which didn't fail to remind me of smash too.
I may overanalyze and be blinded by my desire to see her in though
https://www.youtube.com/watch?v=XYhNzTfP0Og
I could clearly see the begenning of Shantae's trailer with Mimic making his way to wherever Shantae spent that ultimate slumber party ( Risky's ship it seems ) early in the next day's morning to hand her that prized invitation for smash with all her proud friends around. Risky would snatch the invitation and kick everyone out of the boat with the help of Pirate K.Rool and tinkerbats before leaving the harbor. She'd have a victorious laugh before finding out that Shantae somehow managed to make it on top of the mast as a monkey. She'd turn back human again and throw K.Rool in the sea with a salty hair-whip before going face to face with Risky... who would be playable as well in a perfect world hahaha