Under the siege of a large number of zombies for 20 minutes.

You can choose a different career start.
After entering the game, a large number of zombies will besiege you.
You need to destroy them quickly and pick up the experience ball.
Reasonably select active skills or passive skills when upgrading.
There are currently 12 active skills.
12 passive skills.
After the active skill reaches the full level. You can evolve active skills by defeating the boss and dropping props.
Active skills will be more powerful after evolution.
Holding out for 20 minutes in front of hordes of zombies is victory.