Volcanic Snail

Iron Shell. The snail's shell is made of tempered iron from it's proximity to magma and lava. When the snail curls into it's shell it is granted a +5 to AC. 

Magma Trail. The snail absorbs magma and lava as it travels and expels it when in danger. Every time the snail moves the space it just left becomes difficult terrain and induces 2d8 fire damage to all creatures that pass through it for the next five minutes. 

Magma Spray. As an action, the snail can spew acid at a target up to 30ft away. This requires a DC 16 Dex save or the creature takes 2d8 fire damage, a successful save halves the damage. 

Grappling Climb. The snail can attempt to grapple and climb up a creature within 5ft of it. If the grapple is successful the snail can expel it's magma trail on the grappled creature as a move action, resulting in 2d8 fire damage that ignore fire resistance and is halved by fire immunity. While grappled, you can move but at half speed as the intense heat from the magma. 

Swarming Grapple. Up to five snails are capable of grappling the same creature as another snail, in doing so, both snails can utilize their Magma Trail on the subdued creature. When grappled by a second snail the creatures speed is reduced to one quarter (minimum 5ft) and if grappled by a third snail the creature is unable to move until they're capable of breaking the grapple of at least one snail. If five snails manage to grapple a creature, the creature must make a DC 18 Con save or be paralyzed from the intense heat. 

Curl Up. As a reaction, the snail can curl up into it's shell. Doing so grants immunity to fire attacks and resistance to bludgeoning, piercing and slashing damage. In addition, it grants the snail +5 to AC. To uncurl, the snail must utilize 5ft of movement from it's next turn, if the snail is subject to a condition that prevents movement, it will not be able to uncurl.