A new event was just launched called Revelation. It's comprised of 3 Missions that grant skulls (event currency) and when you collect enough of them, you unlock prizes.
This video shows what the 3 Missions look like at CC5
This video shows the 3 new units you can unlock
There are two recurring events where you can earn rare items.
Strike BattleEditStarting on Wednesdays at 10:00 AM PDT (Pacific), for 24 hours you can earn Strike cards by securing victories in PvP Battle. Strikes are single-use items used in battle to either call in reinforcements or heavy artillery. Strikes have a low chance of appearing in Bronze crates, a medium chance in Silver crates and you are guaranteed to get a Strike from a Gold crate. You can store up to 3 of the same Strike in your inventory at a given time.
Rise of La MuerteEditStarting on most Fridays at 10:00 AM PDT, for 24 hours you can attack La Muerte Strongholds from your base HUD. The main reason to attack these bases is to earn the blueprint for the Sniper unit and its Critical Components.
This is where you can use your Redeploy Tokens to hit the same instance of a base multiple times and have the damage persist to the next battle. Also, you get a % damage bonus on subsequent tries so the base gets “easier” for each redeployment until you destroy the base. Try to max out on tokens before attacking.