How do I fight the Corrupted Spirits?

For the invasion to be successful for your alliance members, you should keep in mind that each Corrupted Spirit has its own weakness, which you can use as an advantage to create the most effective strategy.
Wan Shi Tong: Vulnerable to Waterbending
Old Iron General: Vulnerable to Earthbending
Hei Bai: Vulnerable to Firebending
Dragon Eel: Vulnerable to Airbending