Advanced Server is used by developers for Beta testing of new features of the game before it comes out of Mobile Legends Original Server. That is why the advanced server has the latest features, new heroes, and even maps of the game. Once you are inside the Advanced Server, prizes and bonuses are automatically given to the players such as skins and Mobile Legends heroes.
It’s basically rewarding players for helping developers test out the updated game before rolling it out to the general public.
Another advantage of using the Advanced Server is the updates. Updates are much faster for players who are registered in the Advanced Server. For example, players will have access to exclusive content that comes with the updates like new skins and heroes before it is released to the Original Server. You’ll definitely encounter some glitches so best to report them so you get the rewards.
Registering in the Advanced Server is free and will not require a player to purchase the account. Meaning you need to have a low ping and a fast internet connection. It’s experienced that the advanced server is laggier than the original, especially while using the mobile connection.
Remember, not all eligible users will be able to access the Advanced Server. Advanced servers limit the number of users, that’s why it is always full. Make it to level 20 and go look for the test server tab under your account settings. Make sure to connect to stable Wi-Fi. It takes time to reach level 20. 
Here we are in the advanced server. Currently updating.
When you successfully enter here, make sure to connect your Facebook, Google Play, or VK account. This way, it will not wipe away your progress and you can switch anytime between the two servers.
So this will be the new loading screen when Dyrroth is released. Currently, there are two heroes under testing here, xborg and dyrroth. Little witch is gone.