[Theory] the ice that freeze the giants belonging too ur or a slayer.

[sexywave]

I think ur was brought back by tartarus and was turn evil, a dragon slayer of ice froze them.

 

[Sir Blades]

I think that anything is possible when it comes to that man's manga. But i dont think it was ur.

 

[Miyata]

cocaine is a hell of a drug!

 

[ssiddiq78]

I dont think its ur or slayers.
As for slayers i cant realy say but there is this no.7 that holds significant importance like,7 dragon slayers, 7/7/777 dragons disappearance, 7 drangons to travel from eclipse gate, 7 years time gap, so i think adding another dragon slayer will messup the no.7 order.
It has to be some kind of lost magic spell or some thing that is related to other 3 ishval gods and tartarus.

 

[KGB Kakuzu]

Cobra mentioned Tartarus and the gates of hell. Traditionally there are 8 circles of hell.


The 8th circle is a plain of ice and coldness. We've already seen that the recent dark guilds and the underworld use very dark magic. I'd assume this is coming from a Tartarus or underworld mage using Hell Ice.

 

[Transcendence]

That would be an insane plot twist.