To get past the giant fish in Silt you'll need to lure it into smashing some rocks. It sounds obvious, but this eel is hard to predict, and it's easy to get led astray by the middle part of the puzzle. There are some different things to possess, some taunting to do and it can occasionally be unclear if you're doing the right thing in slightly the wrong way. So let's take a look at how it all actually works and what you need to do to defeat the the giant eel in Silt.
How to get past the giant fish in Silt
To get past the giant fish in Silt you'll need to lure it into smashing two different rocks - one above, and one below. You need to use yourself as bait for the first rock at the top of the cave, which will access an area where you can possess some fish. The fish will then let you bite through the rope blocking your way, and then another rope to release a rock inside the passage. Once this rock has fallen to the bottom you then need to use yourself again as bait to make the eel smash into it and open up an area below you. That will let you posses a second fish you can use to release another rock and finally defeat the fish in Silt.
Let's take a look at all that in more detail.
Lure the fish to smash the top rock
You'll meet the giant fish in Silt after following a glowing lure for a while. It's obviously a trap, but even knowing that, the eel moves fast and you'll likely get eaten on your first encounter.
Once you've got that out of the way you'll need to lure him up to the bit of rock sticking out at the top of the cave. To help you judge when it's about to strike, the fish's eyes will narrow to a fine point and it will lunge when its pupils are at their smallest.
Possess the fish to bite through the cables and release the rock
Once you've possessed a fish, use it to bite through the cable blocking the upper passage next to the cave. Swim in and you'll find a second cable holding back a rock. Bite through that as well to release it so it falls into the cave below. Now it's time to tempt the fish again...
Lure the fish into attacking the fallen rock
While the possessed fish you control can attract the eel in Silt, I found it never seemed to provoke it into attacking the rock, which is where some people might get confused. Instead, return to your diver body and use that to draw the big fish in. As long as you're behind the boulder when it attacks, it should hit the rock rather than you and smash open a route to another cave further below.
Possess the Hammerhead fish to smash the rock free in the upper cavern
In the cave below you'll be able to possess one of the hammerhead fish. Take them to the upper cave where you'll see a triangular rock you can ram. That will break the surrounding material and cause the rock to fall into a lower position.
Now you can repeat the process again to make to make the fish attack or bite this rock. This time the Hammerhead will lure the eel over, as well as the diver, so you don't need to swap over - just draw the monster in and then nestle in against the rock so it takes the hit instead of you.
That final bite should stun the eel completely. Once it's down it'll lie on the floor and you'll be able to 'possess' it's eye, ending the level and moving you on to the next stage. That will see you transported to a strange area where you'll need to swim right until you find a strange chained structure. Swim in the point when it open up and you're done.
