One of the D-rank frost lizards lay at Frost's feet, decapitated in a single swift motion. Frost's new skill [claw of the ice wolf] slashed through its neck like a knife through butter. Frost lizards had very little defence around the neck area, making it a perfect target for sharp weapons. However normally being able to catch the thing would be an ordeal, most struggled to keep their calm in the face of a massive lunging monster let alone have the strength to slice through it in single well aimed strike. This was the difference in realms.
Frost being of C-rank and being so well matched against the frost lizard made them very weak in his eyes. The yetis were more dangerous given their body's robust thickness and incredible arm strength.
