Six World bosses are added in Argus in patch 7.3. These updated rules are totally different from the previous world boss. Players should complete three Lesser invasion points. Then can get into the big invasion point and get the chance to challenge the boss.
First of all, players will get a quest to unlock the invasion point:

Invasion point has two grades. In addition to the difficulty of increasing, incentives will be increased as well.

Unlocking Lesser Invasion Points:
In order to unlock Invasion Points, players will need to finish Chapters 1 and 2 of the the Argus storyline which ends in  Invasion Point Offensive. After completing this quest, Illidan will offer the new quest  Where They Least Expect It and unlock Invasion Points.

The Lesser Invasion Points can be completed by 3-10 players together. You also can get in by yourself, complete then scene battle and kill the last boss, then you will get Veiled Argunite, Primal Sargerite and Artifact Power. and also have a chance to get a transmog weapon.
Unlocking Greater Invasion Points:
Players must complete the Invasion Point quest chain in order to unlock Greater Invasion Points:
Where They Least Expect It - Enter an Invasion Point and defeat a Legion Commander.
Invasion Point Offensive - Complete 3 Lesser Invasions.

The Greater Invasion Points is also called big invasion point. It can be completed by a team to kill their leader. It will drop 930+ gears and Artifact Power too. Each week you can only pick up trophy once from the leader. You will get achievement Invasion Obliteration if you kill 6 bosses.

Each Invasion Point will last for exactly 6 hours and there will always be 3 active at a time. You can find the portal of scene battle through the world map. Click the portal then you can get in. You will get a weekly reward if you completed three.