Shoat Summon Location and Guide
While you're on World 2, any time after you get the Submarine, you'll be able to get the Shoat summon. In the northwestern portion of World 2 you'll find a small island, on the southern end of this island when you dive underwater with the Submarine you'll find a small cave entrance, which is shown in my screen shots.
Enter this cave and make your way through it, you'll be battling challenging enemies in this location and this is one of the best places to grind on World 2 for this reason. If you decide not to run from the battles in here, take out the weaker caster first then handle the durable rock-dog like creature.
The Stone Dogs are highly resistant to physical and magical attacks but the caster enemies are susceptible to both. The casters also have this super annoying spell that halves the level of someone on your team for the duration of the battle.
Once you make it through the underwater cave and find yourself on Shoat's island, you'll want to run around fighting random encounters until you encounter Shoat. It won't take very long, he'll probably actually be your first random encounter on this island.
For the battle against Shoat it's recommended that you take him out as quickly as humanly possible because he can Stone two members of your party in a single round. If someone does get Stoned in your party, be sure to cure them with a Soft/Gold Needle as quick as you possibly can.
All in all this battle isn't that difficult, Shoat only has 5000 HP in total so he realistically could be taken out before he even gets a chance to Stone even one member of your party.