The Sky is Fallen Achievement in Guardian Heroes
The Sky is Fallen20
Defeat the Sky Spirit in Story Mode.
How to unlock The Sky is Fallen
The path you need to take to fight this boss is 2,1,4,2,1
This boss fight plays out just like the Dirty Schemer achievement boss fight. Here is the strategy used for both.
This is a two part boss fight. The first thing you will need to do is set the undead warrior in berserk mode. At the start of the match hit and then 5 times. This will select berserk mode for the undead warrior. Just hit again to set him in this mode for this fight (putting the undead warrior in berserk mode). The first part isn't as bad as the second part. His attacks are pretty standard you can opt to attack him when the undead warrior starts hitting him to pull off a damaging combo to make this faster. But you will need to keep a good amount of health for the second part. If he is in your column he will dart at you so I suggest switching columns regularly. A flaw in his AI is if he was in the same column you were in he likes to follow you. You can use this you your advantage by jumping into a new column. Then when he appears in your column next to you, his defenses will be down and you can punish him. But other than that method, I suggest to block , and let the undead warrior do the work.
Now for part 2 of the fight. This is where it gets hard since now he is stronger than before and he can do 2-3 heavy damaging attacks at once. You still want the undead warrior in berserk mode. But now you've got to worry if the ground underneath you is glowing. If it is, move away or you will get hit with a powerful tail attack. He also likes to use the same moves the exploding orb enemies use. He likes to fly and use his breath attack. So basically you are just going to block and dodge his blue floor tail attack, and let the undead warrior do all of the work. Now if it is in the air you can do a air attack or just fire a projectile at it and it will go back to the ground, and then the undead warrior will resume his attack.