Gwyllgi whistled as the ball of flame exploded against the side of the shell, and ultimately fizzled out. If she wanted to cook it, she'd have to do better than that. Without anything that burned easily, she couldn't do so from a distance. She grimaced. Well, she still had some aces up her sleeve. First off, she was resistant to acid. It wouldn't melt her like it would a mortal. She cast a spell, enhancing that aspect of herself further. Then, she activated her cloak of embers, and hellish rebuke, heating up everything around her, and surrounding her in a corona of fire. Then, she cast her hellish regeneration on herself. She'd need it.
She dashed in, and wrapped her arms around the snail, and roared, lifting it up with herculean strength, until she was holding it overhead. She would cook it, in person. She winced as she felt the gas, but with her resistances and her regeneration, she could bear it, for a time. One of them would give out first, and it wouldn't be her. The shell started heating rapidly, held over a literal inferno.