Paper.io 3 is basically Paper.io (which we did a review on) except you are on a team. You join and are given a team. Teammates have the same color and cannot kill each other. You also get to pick your color. The button next to PLAY on the title screen. Shown as a minion below. (that button does not work in Teams mode) Select Team fights to go to team mode in the button shown below.
That is all that's different from Paper.io, so go check out the Paper.io review to learn more. https://m.sites.google.com/site/iounblockedgames/paper-io-3
This sounds really cool !