The Achatina is a Knock-Out tame, using the expensive resource of Sweet Vegetable Cake. Using a taming pen is the most suitable strategy, due to the Achatina being found in the Swamps and Redwood Forests, some of the more dangerous areas of the ARK. Plus, because of the size of the Achatina, it is easily able to be carried by all ridable flying mounts, expressing the fact that a taming pen would be the best way to tame this critter.
If you are considering breeding these, go slam your hand in a car door a few times. It will be much less painful. Literally one veggie cake per percent of growth....and it grows slow.. Digests roughly one point of food per second, so feed a cake about one for every 7 mins (during event boost) and it will gain one percent of growth.