Raiden, Astrid and the twins.

As Raiden was sitting down and relaxing, he heard a mental from Rogue asking him on his on the latest riddle. With the mental link still open any thoughts he had on the riddle would be instantly transmitted to Rogue and the others. He then began to think on the riddle.

"Wise and old, the prophet is back. The man is blind, the man is strong. This part is obvious. He is clearly referring to himself.

Through songs and cheers, a leader was born. Younger and not as wise, the man acted. Frightened and unwise. The meaning of this all depends on which leader the riddle refers to and seeing as we do not know that yet it is impossible to dither the meaning.

Sent far below, the wicked witch, where crystal lied. Held secret from generations, untold legends. This bit is clearly referring to the witch from the last riddle implying this is just the second part of the previous prophecy. Meaning the witch is after the crystal that is burred down here, which means the heart beat Astrid heard belonged to her. 

Nobody knew, nobody believed. Years passed, and the leader died, they believed. The leader cheated, surpassing strongest of forces, but came a price. Leader had to believe, accepted, he finally did in that which he never thought possible. He had to hide, he had to lie. Protecting himself later generations, the next kings and queens. Again the meaning of this depends on the leader of which the riddle speaks, until we find that out it seems it will be impossible to figure the whole riddle out. 

Deep below, a secret room, prisons and jails, now arena which held above. Deep below, a secret room, empty, the witch great and powerful, escaped. This is clearly referring to the magic prison the witch was trapped in during the duration of her banishment. 

Book of secrets, book of history, read many times, secrets of crystal inside. This is clearly referring to the note book I found earlier. As Raiden thought about the notebook, the context which he read in the notebook would also be transmitted to the others through the telepathic link, and since Raiden skimmed every page and reading what looked to be important in every page, this would mean Rogue and the others would be able to get a lot of information from it, some of which may be helpful dithering the riddle.

Now he knew, now he feared. Searched many years, missing, gone, the crystal was, no, hidden all along, least expected, deep within. Under Berk once before, now above forever more. Odin's statue, royal guard, protector of cells. Held a gem, not any more. Kept secret, crystal great and powerful. This clearly is refers to the crystal meaning once we find it, it will remain above ground forever, This clearly refers to the statue of Odin on Berk meaning at one point or another that statue held the crystal. 

Had no choice, hidden all along, future kings and queens, Berk, least expected. Home of Kings, home of Queens, home of young prince, wars 
end, thanks to him, prince of queen today. This is clearly referring to past chiefs of Berk. The kings being male chiefs and the queens being female chiefs. The young prince obviously refers to a son of a female chief, and the fact that it mentions today implies it is referring to Kuro. 

Unknown secret lies within, hidden room. The past I speak, the present I talk. Future, I am blind. The hidden room obviously refers to the room we are now clearing out. So any secrets it contains will we will have to uncover after we have cleared it and dealt with the witch whose looking to steal the crystal from us.

Just as Raiden finished thinking about the riddle, they noticed the dragons had finally finished clearing out the room. Raiden then turned all the dragons back to their original form as Raiden, Astrid and the twins searched for the crystal with the help of the dragons.