Today's session has been rather slow-paced: the heroes spent some time in a port, gathering information about the nearby islands, and eventually decided to set sail towards the Silver Monolith, a mysterious structure rising from the depths of the ocean, seemingly connecting water and sky. They performed a travel roll — rolling a d10 since they're in the middle of the ocean — and it came up a 10.
The group is in the mood for a classic "random battle", so the Game Master decides to come up with a dangerous sea encounter: some kind of huge, monstrous beast. Sometimes you just want a straightforward fight.
Finally, regarding Skills: The GM wants this creature to threaten both Player Characters with its weaker attack, ocean jet, so they think about taking Special Attack and giving it multi (2). This seems a bit excessive, so they instead pick Crisis Effect and have the Thornshark gain multi when in Crisis. A nasty surprise, but manageable.
The GM decides to make the creature a bit more special. It's a big flying fish and the heroes are on a boat in the middle of the ocean, so it's given a Unique Action — it can dive underwater and become immune to normal attacks until the start of its next turn or until it loses Hit Points. This Skill could be quite frustrating, but one of the Player Characters is a capable Elementalist and will certainly prove her usefulness here. She has the bolt-type spell Thunderbolt, which she can use to force the thornshark out of the water and down on the ship's deck.
Finally, the creature is given Damage Immunity to ice damage — let's hope the Player Characters spend a turn Studying this big fish and don't waste any of their precious resources on frost attacks!