Re: infinite infinity chest coins?!
Pre patch you got two things, I'm pretty sure you don't anymore. I've played it enough times and quite often gone through every single IT item in my sticker book to see if I got two items.
There have been occasions where I've not opened the chest due to lag, occasions where I've opened the chest 4-5 times in a row and got coins ranging from 15-30k, and the other night I opened it and got absolutely nothing...yes, nothing. The friend I went in with got absolutely zilch that run as well, he made a post about it, I can't be bothered with it.
As others mentioned, getting Infinity Infinity Chest requires 25k shards, but only gives the highest chance of a legendary. You could play the mode 12 times over and get coins, or you might play 12 times and unlock every party piece. Due to many issues, lag, crashes, and even issues regarding the chest rewards I would highly recommend staying away from this game mode until it's been fixed.
Sure it it can be addictive, and yes I know you want everything but when you're using stars each time and not getting rewarded accordingly it hurts. I did make a thread suggesting a new and better reward system, but you might need to search for it...
I have literally played that game mode over 50 times since the patch just to help friends and well, I'm even more frustrated than they are when they don't get rewards, I was lucky enough to play before the patch and unlock all my characters and yes sometimes I got multiple pieces. It isn't fair on others who missed out on that, patch notes didn't really mention bugs and glitches much so nobody really knows if it was bugged before or if it's bugged now.
Good luck 🙂