These guys have X variants on genesis 1 and they have high torpor so be prepared. To tame them i suggest using a bloodstalker or a basilo that can tank some damage. If you using a bloodstalker stay on water surface and shoot tranqs, when it swims away go underwater and use your crossbow or harpoon. If you use basilo just let it tank it and shoot it with crossbow or harpoon. But be careful about them attacking you cuz these guys are no joke. They usually have a friend near them so you might have to kill the other one in order to tame the you want. When tamed these guys have pretty high damage scaling but lower hp. They have second attack which does bleed damage(scales with damage, wilds also have this attack) they are fast battle creatures and they have pack bonus just like megalodons so get yourself 5-6 xiphactinus and do the hunt missions with them. Hope this helps