Hirukon

Hirukon
Triggering Hirukon requires Aurelid Lure.
To obtain it, you must first fish up Strange Goop from Hirukon’s waters (this appears to be a very rare chance currently).
Taking it to Baroness Vashj will reveal she can make you a lure for Hirukon, and provides a hint as to where you can find the other 3 ingredients.
Pungent Blobfish is fished up from a Pungent Blobfish Cluster inside Coilfang Reservoir at /way #102 52.2 37.9
Flipper Fish is obtained by initially fishing up a Flipper Fish from a Flipper Fish School in Zin-Azshari, Nazjatar at /way #1355 72.8 24.3, which immediately “slips away” and summons a Flipper Fish that flops about and must be caught by clicking on it to get the final item.
Coilclutch Vine is obtained from Coilclutch Vine in Nar’shola Terrace, Shimmering Expanse at /way #205 34.7 75.0, located on the balcony of a tower on the second level of ruins (it’s extremely hard to see it).
Once you have all of these ingredients, return to Baroness Vashj, and she will turn them into an Aurelid Lure.

Despite what the use effect says, right-clicking the Aurelid Lure will consume it and apply Aurelid Lure to you, which allows you to see an Aurelid Cluster to fish in at /way #1970 51.86 74.31, which in turn will trigger Hirukon on a successful fish for a seemingly guaranteed drop of Deepstar Polyp for you on kill. It can drop for non-lure users, but it’s a very low drop chance.

The trigger happens at the same time as looting your bobber, and there will be a zone wide broadcast of “Hirukon cautiously emerges from the depths below.” when it starts rising up.