Board Thread:Speculation House/@comment-27404492-20170918133425/@comment-26397825-20170926122145

The reason the dragon was frozen could be put down to old power vs untrained power. We know that particularly strong SEW could kill ‘’lesser’’ Grimm with just a look...but the Dragon was not a lesser Grimm. It was an older Grimm that had been growing stronger all that time it was stuck in the mountain, so even Ruby’s initial untrained burst wasn’t enough to kill it properly. Instead it got ‘frozen’ and will likely ‘’unfreeze’’ in the future and have to be dealt with again.

As for why it hurt Cinder; she is the host for the Grimm. Her human nature provides a shield for it, allowing it to survive the blast. But just like an armouring shield gets damaged when struck with a sword, Cinder’s body got damaged shielding the Grimm beetle from Ruby’s Silver Eyes.