Freeze them all is a great description of what happens next. The Ogres meet up with the defenders at the top barricades, causing [Pestilence] to rapidly spread through their ranks thanks to Vala. Then Nathaniel calls forth Blighted Paladins into the Ogres closest cluster of Shamans, causing chaos in the ranks as the charge falters and Ogres turn to defend their healers.
Her instructions to wait for the proper timing complete, Laura leaps into the air and the pair of Dragons lay down a stream of Ice Fog the length of the river valley. This had the unintended effect of freezing the river, letting even more Ogres advance, but Cain is dropping lightning Arrows into them, killing dozens a second and spreading Pestilence from the back side while the Plague Mages curse them with [Cripple] causing the lingering damage to thin the tanks even more.