You really do rack it up fairly fast in multiverse. If nothing else…do the regen token one every time it comes up and try to use your ultimate (full meter L2 plus R2) as the finishing blow while not dying each match to maximize score (final score effects box count). Look at your daily quests before this and try to do that stuff in match too. For just a few minutes of play time you will earn 3 to 6 boxes plus a regen token (very good to stockpile them). That is roughly up to 27 gear/shades/abilities plus a regen.
FYI, loot is tied to level when you get it, so no reason to bank boxes. It is however good to level heroes as much as you can before getting a pile of boxes. You get a fair number of levels across many characters by doing story mode. So, it’s a good idea to play story first (but still do the regen token multiverse each day or whenever it comes up as it’s timed-- I see it every night though). Plus, the story is top tier for a fighting game.
Really. I suppose it’s possible to not get into building up your heroes, but give it a whirl. You might be surprised how much fun you are having watching them grow while going for boss challenge multiverses for that epic piece-- now that you know where to look. I find it pretty neat now that I’m tinkering in multiverse.
Edit: oh and if you just want random fights with different looks, you can select random gear in one of the versus menus. This will randomly kit out each fighter at select.