Carl's usual answer to an incoming blast, and the first thing he rules out against a god's axe.
Watching Grull lift Grull's Axe again, Carl works out that the blow will not hit him but will land close enough to kill him — and that his Protective Shell spell will not help him this time. Ruling it out is what forces him onto his last trick, Mordecai's Special Brew, and thirty seconds of being broken and healed instead of shielded.
Carl's standard defensive spell, insufficient against divine-scale damage.
Also appears in books you've already read — spoiler-safe to their endings: