We get the ARMS reveal on Monday 22nd in the morning,...
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and later after Crash Bandicoot 4: It's About Time is revealed at the Summer Games Fest showcase around 30 mins to an hour later, Geoff saves the day (like in 2018) with a surprise reveal of Crash Bandicoot joining Smash Bros. Ultimate.
Thinking on this possibility just a little while ago, I saw certain parallels between the first, and second fighters pass. Although Piranha Plant is not part of the first Fighters Pass, she is still a DLC fighter, and is shown as the first DLC fighter on the SSBU website. Being a character from a Nintendo IP, it sort of mirrors with this second Fighters Pass, with the ARMS rep being the first CP (another Nintendo IP). Now, the second DLC fighter (yet first CP from the first Pass) was revealed during The Game Awards 2018; Joker from Persona 5, a third party IP (from Atlus). Again, with the second fighters pass, we could be in for its parallel scenario with a potential CP 7 reveal during Monday's Summer Games Fest Showcase.
This is all just some food for thought/speculation. For the moment, we wait for the ARMS rep on Monday.