You do not need to use grapples in the ferox cave. Just jump in the water after the ferox enrages. If you have a bloodstalker hanging on the wall out of the attack range of the ferox will aggro it. You're welcome for saving your grapples.
Fjordur Cave at 20, 8 these things spawn at up to 280. Get a desmodus, pick up the ferox, and bring it to the indoor castle nearby. You can just cling to ceiling and come down and feed. Super easy taming on fjordur
As of 3/28/20. Ferox will tame at the wrong level but once put in cryopod will correct to tamed level. A live 145 changed to 217 once in pod post tame. Also dododex is not accurate on x3 possibly x1. The same 145 took 20 element for full tame. At 5% per element.
For tamming you can feed it the element then use the net gun as soon as it changes to hold it in place and you won't have to run around from it . When it shrinks the net dissappear and you can just repeat the process.