These are what I finished for Online:
* Claim 10 smash tags.
* Complete 50 Quickplay battles.
* Defeat an opponent with a higher Global Smash Power than you 5 times in Quickplay.
* Get 3 KOs in a single Quickplay battle.
* Participate in 10 arena battles.
* Use at least 10 different fighters in Quickplay.
* Use at least 30 different fighters in Quickplay.
And here's what I'm aiming for:
* Complete 100 Quickplay battles.
* Complete 200 Quickplay battles.
Also I'm 20 matches away from finishing the "200 Together Mode matches" challenge, I selected level 1 CPUs, put us in the Small Arena, disabled items and set the CPU's health to 10%, then I just dashed while listening to Disney+ shows in the background.