Leon didn't have time to create his steel spears, so he used the steel fists he kept with himself just in case. The kid's mist was fast, but it was an Area of Effect magic, it wasn't fast enough to chase Leon while he was flying. So, Leon just flew in circles around that party while attacking them with the steel fists. Making sure to hit their faces as much as possible, Leon made them focus too much on his direct actions that they didn't notice Leon's indirect actions. While they were busy trying to block and evade the steel fists, Leon slowly covered their bodies with earth.
Leon's plan worked well, almost… the kid noticed Leon's actions and made him lose control over the earth that covered his body by freezing it. Although the ice was very powerful, the kid didn't feel anything.
"I guess he increased his Ice Resistance while he practiced his skills…"