You can get rewards for watching video ads. There are several places in the game where you can do so:
Boxy
Boxy appears on the main game screen at team level 18:
Boxy shows ten video ads every day. The first five videos appear at 5:00 AM your in-game time, and the next five — at 5:00 PM.
Theater
The Theater unlocks once you complete the tutorial. You can find it by tapping Merchant on the main game screen:
At the Theater, you need to watch video ads to get Tickets. You can spend Tickets to buy energy, Raid Tickets, emeralds, and gold. You can earn up to eight Tickets daily.
Keep in mind that you cannot refresh the Theater, and goods are always the same.
Expedition
You can find expeditions in the Airship. To start this expedition, you need to watch a video ad. The expedition lasts six hours, does not require heroes, and has a unique icon on the map:
Exchange Shop
You can watch a video at the Exchange Shop every eight hours and get gold without spending emeralds. This exchange also counts in the progress of daily quests to use Emerald Exchange. However, it neither reduces the number of Emerald Exchange attempts nor increases the number of emeralds needed for an exchange.
Hero Skill Points
You need Skill Points to level up hero skills. Watching a video ad every eight hours is one of the ways of earning Skill Points. You get 10 Skill Points for free for each video you watch:
Note
There is no limit to how many Skill Points you can get for watching videos or spending emeralds. Thus, you can have more than 20 Skill Points available at a time.