Events are weekly side games that are played separately from the main game for a limited time. Players must first be at Rank 8 or higher in order to participate in events.
Note: some info in this article discusses content that has not been released yet. It can be found on the Mission Tracker, and has the possibility of changing before release. Please keep this in mind.
There are currently 9 events in the regular rotation: Japan In Jeopardy, Aztec AdVenture, Egypt Extravaganza, Scandinavia Scramble, Musical Mischief, Incredible Innovation, Impressive Infrastructure, Awesome Architecture, and Compelling Careers.
One important part of doing well in the events is to be active. It's important to start the events as soon as possible after they begin and play often enough to claim mission rewards, invest resources & people, upgrade heroes and claim free capsules. If population missions take longer than production missions, it's best to stay on the event to claim Time Pods for more people. If production missions take longer, it's best to be off the event until the missions are done (provided that the bottom generator in the relevant age(s) are population limited) because offline production is calculated differently than when online, and in a way that gives you more resources. Some events have the same type(s) of missions the most difficult the most often. In those events, prioritize the heroes that help with those missions.
There is a Mission Tracker created by Zephyron that you can use to plan ahead regarding when to upgrade heroes (for spend EXP or level up cards missions) and when to open free capsules (if a collect cards mission is coming soon, save the free capsules for the mission unless they will be maxed for too long by doing so). You can also use its calculator function to determine how long other types of missions will take, which is very useful if you want to take advantage of the offline production algorithm and complete missions as quickly as possible. Since capsule rewards increase with each rank, you may want to save free capsules and big mission capsules for the next rank if doing so is feasible.
There are 3 types of events: short, normal, and long.
Short events include Innovation, Infrastructure, Architecture, and Careers. These events are easy and can be consistently completed with little to no spending. In Innovation and Careers, it is important to be wise with your EXP spending, especially if you spend 50 gems or less on EXP, since capsule EXP is low and there are many EXP-related missions. These events last for 52 hours or 76 hours.
Normal events include Japan, Mexico, and Scandinavia. 2 of these events (Japan and Mexico) need a reasonable amount of gem spending to complete. The amount of spending is low enough that it is worth it for the rewards. You cannot complete these events for free unless you have extremely good RNG. Scandinavia is the easiest event in the game and can always be completed for free, even with bad RNG. These events last for 100 hours.
Long events include Music, Halloween, Christmas, and Egypt. These events last for 148 hours or 268 hours. All events in this category are nearly impossible to complete. To complete long events, you need to buy bundles (likely multiple) with real money and spend a ton of gems. The amount of spending is far more than what the rewards are worth, so I don't recommend it, unless you have another reason for completing them besides rewards.