The Dire Eel: A Phased SoloThe battle takes place as the characters are sailing off the shore of a tropical island, above a coral reef, looking for the eel. To find it, they need to make the following skill checks using an appropriate Investigation skill (such as Perception to see it, Nature to know its habits, or Athletics to swim down and look for signs of it, or Streetwise to chat with other sailors for hints). A character who fails can no longer make attempts, and if all characters fail before success, the eel finds them first...and gets a surprise round.
The battle continues in phases:
Phase I: The Curious Eel (58 hp)
The eel swims beneath the water, investigating the ship and these unusual creatures, and wants to see if they are a threat, or food. It is largely immune to PC attacks while underwater (the water breaks line of effect), though the ballista on the ship can hit it (those proficient in the crossbow can add their proficiency bonus to ballista attacks, others are just rolling ranged basic attacks). The ballista deals 2d8+4 damage to the eel (no ability modifiers). A character can "delay" their attack to trigger when the eel surfaces to attack, but the eel's attacks are entirely underwater at this point.
On each of its turns, the eel attacks the ship. This causes the ship to shake violently (+9 attack vs. Reflex, no damage, but if hit, the character on falls overboard). Overboard characters are attacked more directly by the eel's bite(+11 vs. AC, 2d10+11 damage and the character is grabbed. They must escape or be missed, and make a DC 23 Athletics check to swim back to the ship, +2 to the roll for each square of movement granted by any powers used on them), who ignores the ship in favor of the struggling prey.
Once it takes some damage, it moves on to its next phase.
Phase II: The Angry Eel (58 hp)
The eel surfaces to attack the deck of the ship directly! It rears up and blasts electricity, attacking all characters on deck (+9 vs. Fortitude, 1d10+10 damage and the creature is stunned (save ends) if hit, on a miss: half damage, stunned (end of next)). The eel then goes back underwater, and hits the ship.
Every other round, the Eel spends underwater, hitting the ship as above. On its alternate rounds, the eel rises up and attacks a creature with its bite. At this point, until it goes underwater on its next turn, it is vulnerable to attacks. A creature hit by the bite on this round, and who does not escape before the eel's next turn, is dragged underwater when the eel returns, and must swim back to the ship as above.
Pase III: The Clever Eel (58 hp)
The eel blasts electricity again as above, and then submerges itself, and goes to constrict the ship itself -- it will be crushed in 3 rounds (after each of the PC's go, make a note of how the ship is getting worse). The eel is only vulnerable to ballista attacks during the first two rounds, and then is vulnerable to normal attacks. It responds by biting at any creatures who attack it.
After some damage, it gives up. If the ship gets destroyed, though, the eel begins trying to eat creatures in the water as above. The DC 23 Athletics check lets a character find a piece of floating driftwood long enough to catch their breath.
Phase IV: The Worried Eel (58 hp)
When this phase begins, the eel blasts a final blast of electricity as above, and then attempts to escape. The party can pursue it by making a DC 19 Investigation check of some sort (Nature, Perception...anything that could track the creature), with each check allowing the party to keep pace with the beast, making attacks. A failed check means no ballista attack is possible this turn. While submerged, it is immune to attacks that don't come from the ballista, as above.
If the ship is destroyed, the eel cannot be pursued directly, but can be tracked slowly with the same check.
After one round of fleeing, the eel hides in the reef itself. The party must now go in physically after the beast, making a DC 15 Athletics check to swim into and through the lair. Each failed check drains a healing surge from the character, as they begin to drown. Each successful check increases the DC of the next check by +1. Once they swim in, the beast attacks with its bite, but is also vulnerable to attacks. The lair is twisty and turny, however -- after swimming into it and getting attacked, the eel tries to hide in the lair, requiring a DC 17 Investigation check (as above) to locate the eel until its next turn. An eel that cannot be located, can't be attacked. On each of its turns, the eel will bite someone, and try to hide. On each of their turns, the party can attempt to find it (DC 17), attempt to swim to it (DC as above), and attempt to attack it (defenses as above).
When the eel is finally reduced to 0 hp, it releases another electric blast as a final insult, and then floats lifelessly.
Aftermath
The party, once the eel is dead, can haul its corpse back to the boat at a more casual pace, after surfacing and taking in some breath. The boat's crew can help them, and the eel might need to be cut up into pieces to be removed from its lair. If the ship is sunk, the party will need to swim to the nearest island, and many of the ship's crew will be dead -- possibly the losses from this will be a lot greater than whatever award they hoped to get from killing the beast.
This is my patented "phased combat," which I do for big epic solos who I feel work better as cinematic encounters rather than tactical ones. It's worked pretty OK, though keep in mind it deliberately makes a lot of abilities useless for a good chunk of the adventure and challenges characters who might not be very good at things to make skill checks to do things anyway.
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