That was, indeed, unexpected! (Well, not so much the ultimate spell getting shrugged off). It's both amazing and funny to see a comic where a Custodes admitting his own fallibility is not the most shocking thing to happen. Was that the diverted-power cannon blast Ser ordered last time, or did Powers* just ram Khorne with the tank?
Ser's eyes changing color like Rand's when he runs out of magic was a neat detail.
* I'm guessing it's Powers because he was the only one not to be shown as having bailed out last comic, plus it seems like the sort of thing he'd do.