The giant snail (Achatina Acidia Giganteus) is a large snail that can be encountered during the Temple Trekkingminigame. Wearing a snelm will significantly reduce the amount of damage taken, but this does not affect the accuracy of the snail's attack, although this should not be necessary for high level players. Protect from/Deflect Missiles may be preferable to using a snelm if multiple snails are attacking, especially for low level players. Despite the 280 max hit on hard route as stated by Monster Examine, they don't seem to hit over 100 (although they hit harder on followers) and they are one of the easiest combat events in the minigame.
These monsters will shift their aggression to the player if they are attacked while engaging the player's escort. However, if the escort is fighting a snail and the player stops attacking that snail, it will shift its aggression back towards the escort until the player begins attacking it again.
Giant snails will always drop a snail shell when killed, which can be sold to Barlak in Dorgesh-Kaan for 600 coins. When the escorted NPC delivers the finishing blow (make sure to deal some damage), the snail will instead drop a perfect snail shell; this can be sold to Barlak for 1,000 coins and 500 Crafting experience. There is also a small chance the perfect shell would be dropped instead even if the follower did not fight the snail.