The Manta is one of the most frustrating creatures to tame if you don't trap it, as it will become aggressive if you're in it's presence. The best way to tame one is to find a relatively shallow area of water and build a stone pillar trap (with the pillars spaced out tight enough so the rays can't swim through them) and leave a space to lure the mantis in. Then place the final pillars to trap it in and tame it at your leisure with angler gel. You may get hit once or twice while you feed it angler gel, but you can back away if you take too much damage.
They have terrible turning circle, approach one from above and feed it. Then let it swim circles around you. The occasional time it gets close you can predict its attacks, it “bucks” just before the attack, which is the tail swinging underneath. Quick swim up or back avoids it. Be prepared to get dizzy, long time between feeding
Tame a kaprosuchos and swim to one of these bad boys and do it's alternate attack it will grab it in it's mouth. walk onto the shore where its safe and have another person feed it while in the gators mouth (if you unmount it drops it) it wont attack or die because it's technically not on the shore.