There is a version of agar.io which can let you earn bitcoin. However its run as a faucet with advertisements and its not going to get you a lot of bitcoins. But is a fun way to earn bitcoin while playing. Its called chopcoin
definitely there's,it's called chopcoin.io,things work out like agar.io but with bitcoin rewards as being explained by this reddit users "Fiach_Dubh"
and here's his explanation
As a huge agar/bitcoin fan, I've been waiting for an agar bitcoin hybrid forever.
My Experience so far:
Works exactly like the regular agar.io game. I played on the high roller playground for .01 and killed one opponent twice and another opponent once and got a pay out of .0347 so not so bad of a return if you got the skills. However, the arenas are much smaller, and will likely expand if their are more players.
I was able to withdraw .02 to my wallet no problem.
I've also created a subreddit /r/chopcoin and will be posting some video tutorials/games/dates and times for tournaments there.
so excited for this.
EDIT: if you are a nooby start out on the faucet playground to get a feel for the game. There's no cost on this playground, and you can win some satoshi's (up to 3000 Is what I've been getting).
definitely worth it to fill up your free time with something useful,atleast you earn bitcoin even not that much