I broke down and got the game... I'm nowhere near competitive levels. Trying out random characters is fun though. Robin seems fun! I don't really get how to use Shulk though (monado arts??)
As Shulk is my 2nd main, I'll delve deeper into the Arts:
Jump: Increases jumping ability, but also makes it easier to be knocked back. Good at early-mid % after using Buster.
Speed: Increases walking and running Speed as well as horizontal air movement. Decreases damage output and jumping ability. Good to use at high % if Shield has been used up.
Shield: increases Shulk's shield and KB resistance, but decreases walking and running speed, aerial movement, and damage output. Best to use at high %.
Buster: increases damage output, but decreases knockback. Best used when the opponent is at low %. Tilts are more effective than Smashes due to the decreased KB (more combo ability)
Smash: Increases knockback, but lowers damage output. Also lowers Shulk's KB resistance. Best used when the opponent is at high damage and you're at relatively low damage.