To anyone who is struggling with invasion im here to help!
It doesnt take much but if you dont have them specific there are alternatives.
MY HEROES:
The mayor is there for his shatter (purple+)
Angel is there for revive (purple+)
Flash is there for his slow (purple+)
Simba and gerald are there, because they do fantastic damage to trigger the shatter.
All these heroes need to be at least purple to unlock all the important skills.
I hope this helps anyone, and if you have questions i will try and answer them.