What is this?
Island CYOAs were (are?) a fad on /tg/. I know of almost a dozen, and I come across a new one every so often. The idea behind each of them is the same (you find yourself on a spooky island thing, GO) but they differ in the options that they give. They also differ in how many options you can pick before you have to start taking penalties.
This one is not particularly forgiving.
Companion: The Necromancer
Artifact: The Amulet, Possessed Sword
Nemesis: Fear and Madness, The Other
Oh, and The Other gets some choices too, dang it:
Shelter: Gypsy Caravan
Companion: The Other (a different one), the Blackbark Faerie
Artifact: The Sarcophagus
Covenant: Island Guardians
Nemesis: The protagonist
So what have we got here?
Our protagonist has been displaced to some horrible Otherworld. It matters not whether it's an actual island or not, though we'll refer to it as such for convenience's sake. It's a very dangerous place, inhabited by all kinds of horrible things. There was apparently a magi-tech kind of civilization based here, but it's anyone's guess what happened to them.
Perhaps the Island got them. It has a will of its own, certainly. And it's out for the protagonist's blood.
To that effect it has also plucked up two of the protagonists friends. Perhaps the protagonist's appearance here is a fluke, but theirs was certainly not. They have been told that the protagonist is a very, very bad person now, and that killing zem is of the utmost importance. Letting zem live will do nobody any good, but will mean the deaths of millions.
It may hurt them to believe it, but they've been thoroughly convinced that ze's somehow gone down a bad road.
The statuesque servants of the old civilization are at their disposal. The faeries of the Island, who may be connected or have simply moved in after the original inhabitants left, are responsible for conveying the Islands orders, and one of them is accompanying the protagonist's friends to help them on their quest. They are traveling with other humans (who, unlike the faeries, are definitely latecomers to the Island), who are not noteworthy for their combat skills but know the roads of the Island. And one of them has slight precognitive abilities that should be of help.
Should they die by anyone's hand but the protagonist's, the Island will be able to revive them.
But the worst thing is... our protagonist can't be totally sure that they're wrong. The protagonist has fallen in with some potentially bad company, an amoral necromancer whose reason for tagging along is unknown, and has explained the situation to the protagonist. The necromancer is definitely not popular in these parts, though, especially among the undead (of which there are many). And... there are horrible Lovecraftian monsters that like you. Which is probably not a good sign.
Finally, the protagonist is in possession of a thinking sword. It can steadily improve the protagonist's skill over time, but it is also the source of a growing compulsion to kill. The amulet, which confers both physical and mental health, is keeping its influence at bay, but the amulet will be effective for only so long.