Laius scrounged all his intelligence and luck for this moment.
Here's how I think played out. Silverware drew the dragon's lightning.
Laius threw kensuke, scabbard and all since he can't unsheathe, with nightmares attached to them. This is probably what caused the red dragon to squirm. Laius held out on the poison mist, but was lucky enough to have the ice dragon sneeze on him, freezing his otherwise fleshy and susceptible to poison skin. The red dragon is next, and explosion is created. I can't think of how laius survived a point blank explosion, but a byproduct is his unfreeze. Once the barrel breaks open, laius is brought by the waves to the ice dragons body, which he latches onto. You can even see laius as the ice dragon flies up and out the water. It also conveniently happens to fly right by thistles dragon, which he jumps ship to.