In case you haven't heard, y'all have swapped tribes. Check out the announcement and season page for more details on that, because your new tribes will be doing a lot right off the bat.
First, you need to determine leaders; during today's immunity challenge, each tribe will send in votes to nominate a leader. The votes will work the same way as votes during tribal council, except the person with the most votes will become the leader instead of being voted out. Two tribes will still lose each immunity challenge, so the winning leaders will each be randomly assigned to a tribe (one each).
Anywho, onto today's immunity challenge. For this challenge, each of you will have three cannons to launch cannonballs. You may choose to launch it at any of the other tribes by posting below "Launches cannonball at (insert tribe name here)". Once all cannonballs have been launched or we reach 8:30 PM EST tomorrow, the results will be tallied and the two tribes with the least amount of cannonballs launched towards them will win immunity. A simple challenge, but one with the potential for complex strategy (feel free to publicly strategize with other tribes in the comment section below, should you wish).
Good luck, and don't forget both the leader vote and the immunity challenge!