Can someone please explain infinity rewards to me?

All that I know is if you want to unlock party characters lose on wave 26 (infinity infinity chest) and if you want to get the infinity accessories the fastest lose on wave 16 (tralala chest i think). 

I only made it to the second chest (whichever one that is) twice on solo mode, and got infinity hats both times. Honestly, didn't feel either of them was worth the stars spent or time wasted...the infinity times stink IMO.

From my experience, 25k - One Party character piece, 30k+ Full Party Character piece. Believe if you keep it around 15k and up, you'll score an infinite cosmetic item over a coin reward all the time. I could be wrong, but that's just my experience with Infinity time.... which I hate with all my heart and soul for the amount of time put into it.

You do NOT get a full party character from 30k+ shards.  Prior to the first patch it was possible to get two rewards, but after the patch, you only get one.  Like most have said, just die when you get to 26K shards for your best chance to get a party character piece.

LOL infinity rewards are so broken... why do they even exist?

Party characters fine, but cosmetics as well..... just no.